the bagdad reflection sequence as tabular mafic intrusions evidence from seismic modeling of mapped exposures two dimensional seismic modeling of exposed rocks implicates subhorizontal tabular mafic intrusions as the likely cause of the unusually prominent reflections that constitute the bagdad reflection sequence brs these basement reflections from depths of 3 15 km are observed on cocorp and other data to extend for some 100 km across the basin and range colorado plateau transition zone in west central arizona the nearby buck mountains fortuitously expose an upended upper crustal block which is used in this study as the basis for a 12 x 6 km seismic model ray tracing through this model produces synthetic reflections from the numerous proterozoic diabase intrusions occurring in the buck mountains these synthetic reflections approximate the scale geometry and character of reflections observed on the cocorp data indicating that the intrusions in the buck mountains furnish a viable geologic analogy for the brs several lines of evidence argue that the major competing hypothesis that tertiary detachment surfaces cause the brs is less satisfactory although we cannot rule out the possibility that the brs is related to hypothetical tertiary intrusions of similar distribution and structure geologic evidence more directly implies that these reflectors are proterozoic in age if so the bagdad reflections serve as strain markers and can be used to constrain subsequent deformation in the arizona transition zone their relatively continuous nature thus argues against widespread disruption of the upper crust in the transition zone during tertiary extension moreover identification of these reflectors as subhorizontal mafic intrusions may have profound consequences for interpretation of similar reflections observed elsewhere by bolstering the contention that mafic intrusions are an important cause of basement reflections in the continental crust

germanium silicon fractionation in the weathering environment abstract we present a detailed study of germanium behavior in the soil weathering environment as an important step toward using the ge si system as a tracer of silicate weathering processes in both modern and ancient environments intensely weathered soils developed on hawaiian basalts have bulk soil ge si ratios 2 to 10 times higher than fresh basalt e g 10 to 25 mol mol vs 2 5 mol mol soil ge concentrations increase with si and decrease with fe suggesting that ge sequestration is related to accumulation of secondary soil silicates rather than retention in soil fe oxy hydroxides sequential extractions of these soils suggest that ge si fractionation takes place by ge sequestration during the initial precipitation of secondary soil aluminosilicates principally allophane further si loss and changes in mineralogy as these soils age result in little additional ge si fractionation ge si ratios in granitic soils and saprolites are strongly influenced by relative weathering rates of primary minerals kaolinite has a ge si ratio 5 9 mol mol higher than the plagioclase from which it forms 3 1 mol mol whereas accumulation of primary quartz ge si 0 5 mol mol prevents granitic soils from attaining high ge si ratios laboratory synthesis of allophane confirms that ge is preferentially partitioned into the solid phase upon precipitation of secondary aluminosilicates from solution

structure of the wollaston lake reflector trans hudson orogen canada from reflection avo analysis fractured diabase intrusion fluids or silicified shear zone abstract a nearly 160 km long wollaston lake reflector wlr observed in seismic reflection profile s2b of the 1994 lithoprobe trans hudson orogen transect thot in northern saskatchewan canada is among the most spectacular and well recorded features imaged within the crystalline crust based on modeling of its normal incidence reflectivity the observed bright spot reflector was originally interpreted as a series of tabular diabase intrusions in order to further elucidate its structure we reprocessed line s2b and analysed the wlr for the amplitude variations with offset avo by contrast to conventional approximate avo analysis we used the exact zoeppritz equations and considered a thin layer mixed positive and negative polarities reflectivity the results suggest two possible interpretations of the wlr 1 the reflector caused by a massive mafic intrusion as suggested earlier in which case the intruded rocks should have anomalous poisson s ratios of 0 33 and 2 the wlr represents a silicified shear zone with only moderate e g 5 10 alteration of the host rock and 0 2 although both of these models may to some extent co exist within the wlr its brightness sharpness great lateral extent and smooth shape favour the second interpretation in both models a fractured fluid filled zone within a major crustal detachment should have played a key role in the formation of the wlr the association of the reflector with laterally and depth migrating fluids is also supported by magneto telluric measurements of crustal conductivity beneath the wlr analogies from the studies of the kola superdeep borehole russia where free or metamorphic fluids were found at comparable depths also suggest that fluids may contribute to wlr structure and formation

seismic models of a prograding carbonate platform vercors south east france abstract the southern vercors area south east france displays superb exposures of a lower cretaceous prograding carbonate platform these exposures allow a geometrical sequence analysis to be combined with detailed outcrop observations two dimensional seismic modelling techniques were used to determine the seismic response of three of these exposures the montagnette the archiane valley and the rocher de combau the outcrops display prograding and retreating series of clinoforms interfingering with fine grained basinal sediments photographs from different angles of view combined with detailed field observations were used to construct lithological profiles with a resolution of f few metres p wave velocities and bulk densities were measured from cored hand specimens and selected values were assigned to lithostratigraphic units in each profile the vertical incidence modelling technique was then used to compute migrated time sections of reflectivity these were convolved with source wavelets of different frequencies to produce the final synthetic seismic profiles none of the modelled outcrop geometries is correctly portrayed seismically at 25 50 hz frequencies not only do the synthetic seismic profiles show less detail they also show misleading geometries in most seismic models for instance pseudo unconformities are present that correspond to rapid changes in dip and in facies in outcrop furthermore the seismic tool is not able to resolve between stratal patterns punctuated by unconformities and those with gradual shifts in facies belts accompanied by complex interfingering relationships this implies that an unconformity recognized on a real seismic line should not automatically be assumed to represent a true stratal unconformity large outcrops are often used to show the validity of sequence stratigraphy a concept mainly based on the analysis of seismic lines this study however shows that there is no one to one relationship between geometries observed in outcrop and in seismic lines seismic modelling of outcrops therefore provides a means for evaluating outcrop geometries in terms of seismic stratigraphy

chronology and petrogenesis of a 1 8 g lunar granitic clast 14321 1062 abstract a study was undertaken to determine the chronology of a pristine granite clast 1062 from apollo 14 breccia 14321 using rb sr sm nd and 39ar 40ar methods the genesis of the granite as constrained by the isotopic results and trace element characteristics is discussed chronology the rb sr internal isochron is slightly disturbed and yields an age of 4 09 0 11 ae 87 rb 0 0139 ae 1 and an imprecise initial i sr 0 702 008 if two data are excluded the age becomes 4 13 0 03 ae and i sr 0 698 003 the whole rock and mineral separates are extremely radiogenic they yield model ages which are relatively well defined the average model age is 4 12 0 03 ae relative to babi 0 69898 the sm nd internal isochron is also slightly disturbed and gives an age of 4 11 0 20 ae 147 sm 0 00654 ae 1 the 39ar 40ar average age of the non magnetic fraction of the sample yields a slightly younger age of 3 88 0 03 ae k ar constants from steiger and a 1977 the concordancy of rb sr and sm nd internal isochrons with the rb sr model age strongly suggests that the granitic clast formed at 4 1 ae ago in the shallow crust and was later excavated and brecciated about 3 88 ae ago petrogenesis isotopic and trace element data of the lunar granite show large k la and rb sr fractionations small sm nd fractionation and the distinct v shaped ree distribution pattern at the time of crystallization a two stage model involving crystal fractionation followed by silicate liquid immiscibility sli is proposed for lunar granite genesis we propose that the granite can be the immiscible acidic liquid produced by sli from a residual liquid which underwent fractionation of ca 3 of phases with ree distribution coefficients similar to those of phosphate minerals from a highly evolved parental magma with ree contents about twice those of the 15405 85 quartz monzodiorite qmd the extreme scarcity of lunar granitic samples and their young formation ages suggest that they are probably not directly crystallized from the differentiation of the primordial magma ocean our isotopic results and trace elements data from other workers suggest that granites qmd and probably mggabbronorites may be genetically related and may have formed in a plutonic environment similar to gabbro granophyre associations in terrestrial layered intrusions such as the skaergaard intrusions

imaging and interpreting the shallow crystalline crust abstract in the past many tests of high resolution seismic imaging methods utilizing off the shelf technology from hydrocarbon exploration have had only limited success some problems associated with the application of seismic profiling in the shallow crystalline crust differ from those encountered in sedimentary basins perhaps the most fundamental distinction stems from differences in statistical properties of the reflection coefficient time series analysis of power spectra derived from borehole data indicates that the reflection coefficients in the crystalline crust are depleted in the seismic bandwidth relative to sedimentary basins this fundamental difference must be considered in the design of shallow crustal seismic surveys in order to achieve success to a first approximation acoustic impedance variations in sedimentary basins are controlled by velocity changes whereas velocity and density can vary independently in the crystalline crust and changes in density may be relatively more important in controlling reflectivity in certain instances density fluctuations outweigh velocity fluctuations for example physical rock property data from mining districts in the canadian shield suggest that massive fe oxide or sulphide bodies will generate strong seismic reflections

silicic volcanism at ljosufjoll iceland insights into evolution and eruptive history from ar ar dating abstract ljosufjoll volcano is the largest outcrop of silicic volcanic material in the volcanic snaefellsnes flank non rifting zone of iceland the silicic eruptives range from trachytes to alkaline and peralkaline comenditic rhyolites and show evidence for eruption in both subaerial and subglacial environments thirteen silicic eruptive units have been identified and mapped by a combination of field observations and geochemical correlation the trachytes probably formed by fractional crystallisation of a basaltic magma to form an alkali feldspar rich trachytic mush with continued fractionation of the interstitial melt producing low ba and sr rhyolite magma ar ar dating of feldspars and matrix glass or holocrystalline groundmass has been carried out on twelve of the units many units have a complex ar isotopic system with many samples showing evidence for inherited 40ar in the form of feldspar xenocrysts the deduced eruption ages span an age range from 650ka the eruptive history of ljosufjoll probably extends further back than this but the products of previous eruptions have since been removed by erosion or buried a syenite xenolith was dated at 1 1ma indicating that silicic alkaline magmatism has been occurring at ljosufjoll for over one million years eruptions of silicic material at ljosufjoll appear to be more common during times of rapid climate change and fluctuating ice volume

petrology and chemistry of two large granite clasts from the moon abstract pristine granite clasts in apollo 14 breccias 14321 and 14303 have estimated masses of 1 8 and 0 17 g respectively the 14321 clast is 60 k feldspar and 40 quartz with traces of extremely mg poor mafic silicates and ilmenite the 14303 clast is roughly 33 plagioclase 32 k feldspar 23 quartz 11 pyroxene and 1 ilmenite pyroxene and ilmenite are moderately mg rich plagioclase and pyroxene are strongly zoned both clasts are severely brecciated but monomict pristine both have abundant graphic intergrowths of k feldspar with quartz unlike the majority of similar earth rocks both clasts are devoid of hydrous phases the bulk composition of the 14321 clast is similar to those of several other lunar granitic samples but the 14303 clast is unique it bears as close a resemblance to kreep as it does to other lunar granites silicate liquid immiscibility may explain why the granites are low in ree relative to kreep

chemical studies of l chondrites vi variations with petrographic type and shock loading among equilibrated falls to study compositional trends associated with open and closed system metamorphism and or shock induced heating of the l4 6 chondrite parent s we used icpms and rnaa to quantify 51 trace elements in 48 chemically representative fall samples with these data we used graphic and two multivariate statistical methods for examining evidence for compositional differences with respect to petrographic type and degree of shock loading comparisons of mildly shocked s1 s3 l5 and l6 suites 9 and 8 chondrites respectively yield no convincing statistical evidence for a difference in trace element content our multivariate comparisons show a difference on a model dependent basis but yield indeterminate results on a model independent basis compositionally suites of strongly shocked s4 s6 and mildly shocked l4 6 chondrites 26 and 19 samples respectively can be distinguished at statistically significant levels on both model dependent and independent bases in the strongly shocked suite contents of refractory lithophiles are higher and siderophiles and volatiles are lower than those of the mildly shocked suite at moderately p 0 05 to highly significant p 0 01 levels our studies suggest that chemical differences from vaporization and loss of volatiles along with metal silicate partitioning are present from extended cooling of shock heated bodies produced by intermittent impacts especially the massive impact s that disrupted the l chondrite parent s 500 ma ago

origin of a unique impact melt rock the l chondrite ramsdorf we have studied a unique impact melt rock the ramsdorf l chondrite using optical and scanning microscopy and electron microprobe analysis ramsdorf contains not only clast poor impact melt begemann and wlotzka 1969 but also a chondritic portion 60 g with what appears at low magnification to be a normal well defined chondritic texture however detailed studies at high magnification show that 90 vol of the crystals in the chondritic portion were largely melted by the impact the chondrules lack normal microtextures and are ghosts of the original features the only relics from the precursor chondrules are olivine crystals which have the highest melting temperature 1620 c pyroxene rich chondrules were so extensively melted that no phenocrysts were preserved and the melt crystallized in situ before significant mixing with exterior olivine rich melts fine grained pyroxene chondrule ghosts have sharper boundaries with the matrix than porphyritic olivine and pyroxene chondrule ghosts probably because pyroxene rich melts are significantly more viscous complex textures that formed by injection of melt along cracks and fractures in relic olivines suggest that the chondritic portion of ramsdorf formed directly from petrologic type 3 4 material by strong shock we infer that ramsdorf was largely melted by shock pressures of 75 90 gpa and that chondrule ghosts and relic olivine phenocrysts were locally preserved by rapid cooling quenching was not due to the addition of cold clasts into the melt but to heterogeneous shock heating that only caused internal melting of large olivines and pyroxenes ramsdorf appears to be one of the most heavily shocked meteorites that has retained some trace of its original texture

the hsi bright reflector further evidence for extensive magmatism in the precambrian of western canada abstract seismic reflection lines acquired in 1995 as part of lithoprobe canada s national geoscientific research program revealed unusually bright reflectors of extensive lateral scale in the archaean medicine hat block of southern alberta the herein named head smashed in hsi reflector is imaged over an area of at least 6000 km 2 in the upper half of the crust the reflector appears as a mostly horizontal to subhorizontal feature although continuous it has a complex and laterally variable internal structure comparison with a reflector of known impedance contrast in the overlying western canadian sedimentary basin indicates a high impedance structure to cause the reflections dense one dimensional modelling is consistent with the reflector being a multilayered structure with layer thicknesses in the range of tens to hundreds of metres and lateral scales of discrete reflecting elements between tens of metres and hundreds of metres polarity constraints overall geometry and reflection character strongly suggest that mafic ultramafic horizontal sheets are the cause of hsi reflectivity the hsi is the third major sequence of strong crustal reflectivity imaged by lithoprobe deep seismic data in the precambrian crust of western canada all three features are very similar in overall geometry reflector strength and character and have been interpreted as horizontal sheetlike intrusions small scale variations of the reflectivity signatures suggest a pronounced rheological heterogeneity in the upper crustal rocks within the host tectonic domains

precambrian pleistocene tectono stratigraphic evolution of the southern llanos basin colombia the llanos basin located in the eastern region of colombia northwestern south america is an andean foreland basin between the eastern cordillera colombian andes and the guyana precambrian shield the basin is the latest stage of a complex multiphase evolution that began in the paleozoic at the latest a paleozoic pleistocene basin evolution model is presented based on a regional two dimensional industry seismic data set and well log observations for the southern part of the basin five tectono stratigraphic sequences were identified 1 lower paleozoic depocenters preserved along inverted neoproterozoic basement blocks 2 an upper paleozoic marine sequence folded and faulted in the late paleozoic during assembly of pangea 3 upper cretaceous paleocene shallow marine sediments deposited in a distal foreland basin related to uplift of the western and central cordilleras of colombia the sequence pinches out against a paleozoic hinge or foreland bulge area 4 an eocene miocene foreland basin related to uplift of the eastern cordillera resulting in a wedge geometry and 5 pliocene pleistocene fluvial deltaic rocks overfilling the foreland basin reactivation of paleozoic structures occurs at the top of this sequence with the development of anticlinal structures present day stress fields indicate that subduction of the nazca plate beneath south america may be responsible for reactivation of paleozoic structures inversion of north south structures with the neoproterozoic basement is interpreted to be responsible for the paleozoic and pleistocene deformation whereas cenozoic deformation is related to the two main stages of foreland development of the basin to the east where the paleoproterozoic basement is present no deformation is interpreted

reflection polarity of the midcrustal surrency bright spot beneath southeastern georgia testing the fluid hypothesis a small reflection seismic experiment with an explosive source was conducted in southeastern georgia to determine the polarity of an unusually strong midcrustal reflector the surrency bright spot sbs which was found at a depth of approximately 16 km during earlier cocorp profiling in the region in addition to being very bright the sbs is notable for being unusually flat and horizontal for about half of its 4 km length as these characteristics are similar to those of fluid caused reflections at shallow depths it has been suggested that the sbs may be caused by in situ midcrustal fluids if caused by fluid enclosed in fracture porosity in solid rock the reflection would be expected to exhibit a negative polarity from the top of the porous zone the vibroseis data however gave ambiguous results with regard to polarity due to the limited bandwidth and inherent uncertainties about the phase of the source signal the new experiment consisted of four dynamite shots each recorded at three receiver stations by seismic group recorders sgr borrowed from amoco production company comparison of the dynamite records with geophone polarity tests indicate that the sbs is characterized by a positive reflection coefficient at its top this result itself does not negate the fluid hypothesis a fluid fluid interface could cause the positive reflection as well as the flat spot nature of the reflector waveform modeling shows that the sbs is caused by two or more thinly spaced reflectors a relatively high impedance layer about 120 m thick provided a good match to the observed dynamite data but requires a lower boundary having a slightly smaller reflection coefficient than the upper boundary 0 7 versus 1 0 a 150 m thick porous zone model also provided a relatively good fit to the observed dynamite data but in this model the polarity test requires that the initial sbs reflection of positive polarity be caused by a fluid fluid interface within the porous zone and that the top of the porous zone be relatively non reflective though these observations do not preclude the fluid hypothesis they certainly make the high impedance model the simpler of the two alternatives presented here the additional constraints imposed by the modeling also suggest that the sbs is more complex than these simple two interface models in either of these cases wavelet tuning contributes in part to the unusually large amplitude of the sbs reflection

tectonic entrapment and its role in the evolution of continental lithosphere an example from the precambrian of western canada new geophysical data acquired over the buried crystalline basement of western canada provide constraints on the history of tectonic assembly of the western canadian shield in the interval 1 75 1 85 ga specifically these data provide new perspectives on the evolution of an archean continental fragment heame province that was trapped in a tectonic vise between coeval orogenic belts that dipped beneath the hearne province the trans hudson orogen developed along the southeastern margin of the hearne province as a series of ocean floor oceanic arc and arc marginal basins were telescoped and thrust obliquely beneath the hearne along the northwest edge of the hearne collapse and subduction of a narrow marginal basin now marked by the subsurface extension of the snowbird tectonic zone led to formation of magmatic arc and collision of older proterozoic terranes the hearne province itself is characterized by regional granulite grade metamorphism and evidence of extensive and pervasive partial melting of the crust the internal character of the hearne province seen on crustal seismic reflection profiles is that of a crustal scale structural fan with reflection fabrics that verge toward the bounding orogens the deformation of the hearne is predominantly of paleoproterozoic age and constitutes a thorough reworking of this formerly archean crustal domain over a distance of more than 600 km across strike entrapment and thermal weakening of the hearne resulted from mechanical coupling of inferred buoyant subduction collision zones and removal of or modification of archean lithospheric mantle that may have originally formed the keel to the hearne long period magnetotelluric profiles show that anomalously conductive mantle lithosphere underlies the present day hearne province which is attributed to metasomatic modification of the subcontinental lithosphere following collisional thickening and delamination convective removal of thickened lithosphere in the proterozoic tectonic entrapment as illustrated by the proterozoic structural and thermal evolution of the hearne province crust and subcontinental mantle may be an example of the lithospheric consequences of opposing collisional polarity during assembly of continents

silica polymorphs in lunar granite implications for granite petrogenesis on the moon granitic lunar samples largely consist of granophyric intergrowths of silica and k feldspar the identification of the silica polymorph present in the granophyre can clarify the petrogenesis of the lunar granites the presence of tridymite or cristobalite would indicate rapid crystallization at high temperature quartz would indicate crystallization at low temperature or perhaps intrusive slow crystallization allowing for the orderly transformation from high temperature silica polymorphs tridymite or cristobalite we identify the silica polymorphs present in four granitic lunar samples from the apollo 12 regolith using laser raman spectroscopy typically lunar silica occurs with a hackle fracture pattern we did an initial density calculation on the hackle fracture pattern of quartz and determined that the volume of quartz and fracture space is consistent with a molar volume contraction from tridymite or cristobalite both of which are less dense than quartz moreover we analyzed the silica in the granitic fragments from apollo 12 by electron probe microanalysis and found it contains up to 0 7 wt tio2 consistent with initial formation as the high temperature silica polymorphs which have more open crystal structures that can more readily accommodate cations other than si the silica in apollo 12 granitic samples crystallized rapidly as tridymite or cristobalite consistent with extrusive volcanism the silica then inverted to quartz at a later time causing it to contract and fracture a hackle fracture pattern is common in silica occurring in extrusive lunar lithologies e g mare basalt the extrusive nature of these granitic samples makes them excellent candidates to be similar to the rocks that compose positive relief silicic features such as the gruithuisen domes

syn tectonic magmatism and the development of compositional layering ungava orogen northern quebec canada abstract layer and foliation parallel emplacement of granitic veins was an important process in the regional development of compositional layering in now exhumed middle crustal sections of both archean and paleoproterozoic age in the northern ungava peninsula quebec canada in the archean superior province diorite and tonalite plutons were penetratively deformed and metamorphosed at granulite facies conditions coeval with voluminous granitic magmatism the paleoproterozoic narsajuaq arc contains evidence for contemporaneous magmatism transpressional deformation and granulite facies metamorphism prior to its collision with the superior province basement in both plutonic domains regional compositional layering is defined by 1 metre to kilometre scale alternation of generally well foliated tonalite and quartz diorite bodies and 2 centimetre to kilometre scale variably deformed granitic veins and sheets that lie parallel to layering tectonic foliation in the host rocks syn tectonic intrusion of a substantial portion of the veins along extension fractures sub parallel to layering foliation i e at high angle to the regional shortening direction is interpreted to have occurred due to the combination of a strong anisotropy and high magma pressures compositional layering generated and or enhanced by this process may contribute to the overall seismic reflectivity of the middle and lower crust

non mare silicic volcanism on the lunar farside at compton belkovich non basaltic volcanism is rare on the moon and has been found predominantly on the lunar nearside analysis of lunar reconnaissance orbiter camera images and spectral data reveal the presence of compositionally evolved non basaltic volcanism on the lunar farside

seismic reflection investigations of the mount cayley bright spot a midcrustal reflector beneath the coast mountains british columbia an unusually high amplitude midcrustal reflector was discovered by a lithoprobe seismic reflection survey crossing a predominantly plutonic region in southwestern british columbia canada the bright spot was observed adjacent to mount cayley a large quaternary volcanic center associated with the cascadia subduction zone magmatic arc characterization of the bright spot may advance our understanding of either the midcrustal structure of magmatic supply systems or the presence and storage of saline fluids in the midcrust the location and three dimensional geometry of the reflector were determined using travel time inversion the resulting suite of models consistently describe a northwest dipping reflector that lies 12 5 to 13 km beneath the mount cayley volcanic complex the areal extent of the reflective surface is 3 km by 1 km and the structure is less than 1 6 km thick the transition between the body and the country rock must be rapid 200 m and exhibit a large impedance contrast in order to generate reflections of such high frequencies 30 hz and relative amplitudes 8 0 db our preferred interpretation for the reflector is a fossil sill complex associated with the volcanic development of mount cayley however the data do not rule out the possibility that the reflective structure represents melt lenses or saline fluid produced by the dewatering of the subducted slab the mount cayley bright spot lies just below the brittle upper crust as do the midcrustal reflectors detected beneath japanese subduction arc volcanoes this correlation suggests that thermal and rheological properties just below the brittle ductile crustal transition may be favorable for reflector formation

a comment on titaniq under pressure the effect of pressure and temperature on the solubility of ti in quartz by jay b thomas e bruce watson frank s spear philip t shemella saroj k nayak and antonio lanzirotti trace concentrations of ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the titaniq geothermobarometer of thomas et al contrib miner petrol 160 743 759 2010 it utilises the partitioning of ti into quartz as an indicator of the pressures and or temperatures of crystal growth for a given value of tio2 activity in the system if temperatures are inferred to 20 c pressure is constrained to 1 kbar and vice versa there are significant contrasts however between the conclusions from titaniq and those for natural quartz as well as other mineral phases in volcanic rocks application of the titaniq model to quartz from the 27 ka oruanui and 760 ka bishop high silica rhyolites where the values of t p and tio2 activity are constrained by other means fe ti oxide equilibria melt inclusion entrapment pressures in gas saturated melts melt and amphibole compositions yields inconsistent results if realistic values are given to any two of these three parameters then the value of the third is wholly unrealistic the model yields growth temperatures at or below the granite solidus pressures in the lower crust or upper mantle or tio2 activities inconsistent with the mineralogical and chemical compositions of the magmas cl imagery and measurements of ti and other elements in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals but direct linkages to p t conditions during crystal growth cannot be achieved

crustal structure and reflectivity of the swiss alps from three dimensional seismic modeling 2 penninic nappes surface geological mapping laboratory measurements of rock properties and seismic reflection data are integrated through three dimensional seismic modeling to determine the likely cause of upper crustal reflections and to elucidate the deep structure of the penninic alps in eastern switzerland results indicate that the principal upper crustal reflections recorded on the south end of swiss seismic line nfp20 east can be explained by the subsurface geometry of stacked basement nappes in addition modeling results provide improvements to structural maps based solely on surface trends and suggest the presence of previously unrecognized rock units in the subsurface construction of the initial model is based upon extrapolation of plunging surface structures velocities and densities are established by laboratory measurements of corresponding rock units iterative modification produces a best fit model that refines the definition of the subsurface geometry of major structures we conclude that most reflections from the upper 20 km can be ascribed to the presence of sedimentary cover rocks especially carbonates and ophiolites juxtaposed against crystalline basement nappes thus in this area reflections appear to be principally due to first order lithologic contrasts this study also demonstrates not only the importance of three dimensional effects sideswipe in interpreting seismic data but also that these effects can be considered quantitatively through three dimensional modeling

trace element and textural evidence favoring lunar not terrestrial origin of the mini granite in apollo sample 14321 abstract the 14321 lunar granite 14321g has recently been reinterpreted bellucci et al 2019 as a piece of the hadean earth impact transported to the moon in principle samples of such derivation may afford important insights into the nature of earth s hadean crust we have tested the terrestrial provenance hypothesis by comparing trace element data from 14321g versus other lunar evolved rocks and a large data base for terrestrial granites volatile trace metals zn ga and ge are depleted in 14321g below the terrestrial granite ranges and relative to the terrestrial granite averages by factors of 27 2 0 and 18 respectively evidence from shocked chondrites martian meteorites and impact shock studies in general indicates that such major depletions are unlikely to develop without near complete shock melting which clearly did not occur in the mostly still crystalline 14321g moreover other aspects of compositional disparity between 14321g and terrestrial granites involve exclusively refractory trace elements compared to terrestrial granites of similarly high ba content 14321 is enriched in ta by a factor of 10 and the few terrestrial granites that are as ta rich as 14321 have 10 times lower ba the refractory element ratio lu sm is also close to 10 times higher in 14321g than in terrestrial granites of similarly high ba content other highly evolved lunar rocks felsites strongly resemble 14321g in all these respects we conclude that 14321g is probably of wholly lunar derivation this finding stands in contradiction to a recent inference from ti in quartz modeling bellucci et al 2019 that 14321g crystallized at a pressure of 0 69 gpa the geodynamically limited moon was presumably never capable of forming or burying such a highly granitic material 100 km below the base of its crust nor of excavating material from such a depth to the surface

ejection of martian meteorites we investigated the transfer of meteorites from mars to earth with a combined mineralogical and numerical approach we used quantitative shock pressure barometry and thermodynamic calculations of post shock temperatures to constrain the pressure temperature conditions for the ejection of martian meteorites the results show that shock pressures allowing the ejection of martian meteorites range from 5 to 55 gpa with corresponding post shock temperature elevations of 10 to about 1000 c with respect to shock pressures and post shock temperatures an ejection of potentially viable organisms in martian surface rocks seems possible a calculation of the cooling time in space for the most highly shocked martian meteorite allan hills alh 77005 was performed and yielded a best fit for a post shock temperature of 1000 c and a meteoroid size of 0 4 to 0 6 m the final burial depths of the sub volcanic to volcanic martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for martian meteorites during the impact of a small projectile 200 m as defined by numerical modeling artemieva and ivanov 2004 a comparison of shock pressures and ejection and terrestrial ages indicates that on average highly shocked fragments reach earth crossing orbits faster than weakly shocked fragments if climatic changes on mars have a significant influence on the atmospheric pressure they could account for the increase of recorded ejection events of martian meteorites in the last 5 ma

titaniq recrystallized experimental confirmation of the original ti in quartz calibrations several studies have reported the p t dependencies of ti in quartz solubility and there is close agreement among three of the four experimental calibrations new experiments were conducted in the present study to identify potential experimental disequilibrium and to determine which ti in quartz solubility calibration is most accurate crystals of quartz rutile and zircon were grown from sio2 tio2 and zrsio4 saturated aqueous fluids in an initial synthesis experiment at 925 c and 10 kbar in a piston cylinder apparatus a range of quartz crystal sizes was produced in this experiment both large and small examples were analyzed by electron microprobe to determine whether ti concentrations are correlated with crystal size cathodoluminescence images and epma measurements show that intercrystalline and intracrystalline variations in ti concentrations are remarkably small regardless of crystal size the average ti in quartz concentration from the synthesis experiment is 392 1 ppmw ti which is within 95 confidence interval of data from the 10 kbar isobar of wark and watson contrib mineral petrol 152 743 754 2006 and thomas et al contrib mineral petrol 160 743 759 2010 as a cross check on the ti in quartz calibration we also measured the concentration of zr in rutile from the synthesis experiment the average zr in rutile concentration is 4337 32 ppmw zr which is also within the 95 confidence interval of the zr in rutile solubility calibration of ferry and watson contrib mineral petrol 154 429 437 2007 the p t dependencies of ti solubility in quartz and zr solubility in rutile were applied as a thermobarometer to the experimental sample the average ti in quartz isopleth calculated from the calibration of thomas et al contrib mineral petrol 160 743 759 2010 and the average zr in rutile isopleth calculated from the calibration of tomkins et al j metamorph geol 25 703 713 2007 cross at 9 5 kbar and 920 c which is in excellent agreement with the p t conditions of the synthesis experiment separates of the high ti quartz from the initial synthesis experiment described above were used as starting material in subsequent experiments at 20 kbar at which pressure the solubility of ti in quartz is expected to be significantly lower in the recrystallized quartz these recrystallization experiments were conducted under wet and dry conditions at 925 c and under wet conditions at 850 c both wet and dry recrystallization experiments produced polycrystalline quartzites rutile occurs as inclusions in quartz and as individual crystals dispersed along quartz grain boundaries quartz that grew during the recrystallization experiments has dark cathodoluminescence indicating substantially lower ti concentrations the average ti concentrations in quartz from the recrystallization experiments are within the 95 confidence interval of a linear fit to the 20 kbar data of thomas et al contrib mineral petrol 160 743 759 2010 collectively the results from the synthesis and recrystallization experiments confirm that the ti in quartz concentrations used to calibrate the p t dependencies of ti in quartz solubility in thomas et al s contrib mineral petrol 160 743 759 2010 calibration represent the equilibrium concentrations of ti in quartz

a review of lunar chronology revealing a preponderance of 4 34 4 37 ga ages in this study data obtained from sm nd and rb sr isotopic measurements of lunar highlands samples are renormalized to common standard values and then used to define ages with a common isochron regression algorithm the reliability of these ages is evaluated using five criteria that include whether 1 the ages are defined by multiple isotopic systems 2 the data demonstrate limited scatter outside uncertainty 3 initial isotopic compositions are consistent with the petrogenesis of the samples 4 the ages are defined by an isotopic system that is resistant to disturbance by impact metamorphism and 5 the rare earth element abundances determined by isotope dilution of bulk of mineral fractions match those measured by in situ analyses from this analysis it is apparent that the oldest highlands rock ages are some of the least reliable and that there is little support for crustal ages older than 4 40 ga a model age for ur kreep formation calculated using the most reliable mg suite sm nd isotopic systematics in conjunction with sm nd analyses of kreep basalts is 4389 45 ma this age is a good match to the lu hf model age of 4353 37 ma determined using a subset of this sample suite the average modelmore age of 4353 25 ma determined on mare basalts with the 146sm 142nd isotopic system with a peak in pb pb ages observed in lunar zircons of 4340 20 ma and the oldest terrestrial zircon age of 4374 6 ma the preponderance of ages between 4 34 and 4 37 ga reflect either primordial solidification of a lunar magma ocean or a widespread secondary magmatic event on the lunar nearside the first scenario is not consistent with the oldest ages reported for lunar zircons whereas the second scenario does not account for concordance between ages of crustal rocks and mantle reservoirs less

possible role of midcrustal igneous sheet intrusions in cratonic arch formation 1 factors controlling widespread cratonic arch formation across western north america from the early paleozoic to the middle mesozoic remain poorly understood while a number of causes such as mantle hot spots lithospheric contraction mantle flow and lithospheric flexure due to surface loading have been suggested to explain the localized uplift of basement blocks on otherwise tectonically quiescent margins a variety of mechanisms may be at work here we test the hypothesis that seismically detected packages of discrete midcrustal igneous sheet intrusions impart rheological contrasts within the crust which act as seeds for cratonic arch formation in the presence of weak intraplate compression using finite element modeling of intraplate deformation we find that the seismically resolved sills can generate significant surface uplift in the presence of modest strain rates over reasonable orogenic timescales cratonic arch formation would be enhanced in the presence of additional thin seismically unresolvable sills while midcrustal sheet intrusions may be just one of many factors influencing cratonic arch formation their presence in northern alberta canada can help explain the asymmetric configuration of the well studied peace river arch

raman spectroscopic characterization of h2o in co2 rich fluid inclusions in granulite facies metamorphic rocks abstract water h2o has been identified during raman analyses at 150 200 c of fluid inclusions from granulites that were previously thought to contain pure co2 at room temperature h2o in a co2 rich fluid inclusion forms an optically unresolvable liquid wetting the inclusion walls during heating the h2o phase evaporates into the co2 phase to produce a homogeneous h2o co2 fluid throughout the inclusion volume and the h2o raman peak at 3640 cm 1 is clearly resolvable at elevated temperatures to test and confirm the method synthetic h2o co2 fi of known composition 87 5 mol and 95 mol co2 were also analyzed previously studied granulite samples from the adirondack mountains usa and from the kerala khondalite belt sittampundi complex and sevitturangampatti india were tested for the presence of h2o in co2 rich fluid inclusions traces of h2o were found in co2 rich fluid inclusions in quartz crystals from the adirondacks and from the kerala khondalite belt h2o was not detected in co2 rich secondary fluid inclusions in garnet from the sittampundi complex and from sevitturangampatti rather hydrogarnet was detected along the walls of inclusions in garnet as evidenced by a peak at 3661 cm 1 the hydrogarnet is interpreted to be a step daughter phase that formed by reaction of the h2o in the fluid inclusion with the garnet host during retrogression these observations confirm the presence of an h2o bearing co2 rich fluid at some time during granulite petrogenesis but do not resolve the question of whether these co2 rich fluids were trapped at peak metamorphic conditions or during retrogression or whether the fluid inclusions have reequilibrated following entrapment

interpreting u pb data from primary and secondary features in lunar zircon in this paper we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon u pb isotopic systems and the significance of these features for understanding lunar processes lunar zircons can be classified according to i textural relationships between zircon and surrounding minerals in the host breccias ii the internal microstructures of the zircon grains as identified by optical microscopy cathodoluminescence cl imaging and electron backscattered diffraction ebsd mapping and iii results of in situ ion microprobe analyses of the th u pb isotopic systems primary zircon can occur as part of a cogenetic mineral assemblage lithic clast or as an individual mineral clast and is unzoned or has sector and or oscillatory zoning the age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data a secondary set of microstructures superimposed on primary zircon include localised recrystallised domains localised amorphous domains crystal plastic deformation planar deformation features and fractures and are associated with impact processes the first two secondary microstructures often yield internally consistent and close to concordant u pb ages that we interpret as dating impact events others secondary microstructures such as planar deformation features crystal plastic deformation and micro fractures can provide channels for pb diffusion and result in partial resetting of the u pb isotopic systems

40ar 39ar age determinations of lunar basalt meteorites asuka 881757 yamato 793169 miller range 05035 la paz icefield 02205 northwest africa 479 and basaltic breccia elephant moraine 96008 40ar 39ar data are presented for the unbrecciated lunar basaltic meteorites asuka a 881757 yamato y 793169 miller range mil 05035 lapaz icefield lap 02205 northwest africa nwa 479 paired with nwa 032 and basaltic fragmental breccia elephant moraine eet 96008 stepped heating 40ar 39ar analyses of several bulk fragments of related meteorites a 881757 y 793169 and mil 05035 give crystallization ages of 3 763 0 046 ga 3 811 0 098 ga and 3 845 0 014 ga which are comparable with previous age determinations by sm nd u pb th pb pb pb and rb sr methods these three meteorites differ in the degree of secondary 40ar loss with y 793169 showing relatively high ar loss probably during an impact event 200 ma ago lower ar loss in mil 05035 and no loss in a 881757 bulk and impact melt glass bearing samples of lap 02205 gave similar ages 2 985 0 016 ga and 2 874 0 056 ga and are consistent with ages previously determined using other isotope pairs the basaltic portion of eet 96008 gives an age of 2 650 0 086 ga which is considered to be the crystallization age of the basalt in this meteorite the ar release for fragmental basaltic breccia eet 96008 shows evidence of an impact event at 631 20 ma the crystallization age of 2 721 0 040 ga determined for nwa 479 is indistinguishable from the weighted mean age obtained from three samples of nwa 032 supporting the proposal that these meteorites are paired the similarity of 40ar 39ar ages with ages determined by other isotopic systems for multiple meteorites suggests that the k ar isotopic system is robust for meteorites that have experienced a significant shock event and not a prolonged heating regime

seventh foray whitlockite rich lithologies a diopside bearing troctolitic anorthosite ferroan anorthosites and kreep seventeen nonmare samples most of them pristine are characterized and implications of the new data are discussed five pristine samples are from apollo 14 near the center of the kreep rich zone in the moon s western hemisphere three of them are alkali anorthosites rich in ca phosphate whitlockite which apparently crystallized from magmas with ree contents roughly 6 those of high k kreep the alkali anorthosites probably formed from mg rich magmas that assimilated large amounts of urkreep but some might have formed by metasomatism of ferroan anorthosite by urkreep the gabbronorite norite classification scheme is not well suited to western hemisphere lithologies probably due mainly to the overriding effects of longitude petrochemistry correlations a diopside bearing mg rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic high ca pyroxene rich mg rich magmas and suggests that some source regions of mg rich magmas were relatively ca rich several pristine kreep fragments from apollo 15 station 2 are texturally and compositionally much like other pristine kreep and thus reinforce the evidence that kreep is highly uniform the pristine anorthosites on the other hand demonstrate further that lunar anorthosites are diverse

the s reflector west of galicia the seismic signature of a detachment fault the so called s reflector is a group of bright continuous reflections underlying the landward tilted fault blocks of the west galicia rifted margin s has been interpreted as the brittle ductile transition the lop of an intrusion a detachment fault and the crust mantle boundary to constrain the internal structure of the reflector we have carried out detailed analyses of these reflections we compare the waveforms of the seafloor reflection and its first multiple both to determine the amplitude of the seafloor reflection and to show hat the seafloor is in effect a spike in the reflectivity series so that the seafloor reflection can be used as the far field wavelet including both source and receiver ghosts we compare he waveform of the seafloor and 5 and show that within the resolution of our data s is a reflection from a step increase in acoustic impedance this result is confirmed through complex trace analysis and in particular the determination of the apparent polarity of s and the examination of the instantaneous frequency function s is consistently positive polarity and shows no significant frequency anomaly simple modelling shows that s is very unlikely to be a reflection from a thin layer we thus conclude that s is probably a single steplike interface from the varying frequency content of the data we determine a value for the effective q between s and the seafloor and use this to assess the amplitude loss due to attenuation and scattering we use a comparison between the seafloor and the s reflection to constrain the amplitude of s and estimate a reflection coefficient for s of at least 0 2 in places decreasing landwards by analogy with structures developed in the highly extended regions of the western united states we consider that the most likely interpretation of s is as a sharp west dipping detachment fault separating a granitic upper plate from a higher velocity lower plate locally probably serpentinized mantle

deep 3 d seismic reflection imaging of precambrian sills in southwestern alberta canada abstract a number of bright reflector sequences within the crystalline basement were imaged on 2 d multichannel crustal seismic reflection profiles collected by lithoprobe from 1991 to 1995 one such sequence in southern alberta the head smashed in hsi reflector spans a depth range of 6 21 km with an aerial extent of at least 6000 km2 this series of reflectors and similar sequences in central alberta and northern saskatchewan have been interpreted as packages of horizontal sheet like mafic sills that intruded the precambrian basement hundreds of millions of years after crustal formation in 1999 through our request to extend an exploration survey to longer travel times a partnership group from the canadian petroleum industry recorded a 9 by 6 km 3 d reflection dataset to 8 s two way traveltime twtt at a location southwest of the hsi reflector following processing which included a special procedure to remove strong ground roll that persisted at travel times of interest we identified a sequence of reflections between 4 and 5 s that we correlate with those associated with the hsi reflector however the reflections are not as bright or as continuous as those on the 2 d profiles based on these results and the characteristics of the sills on the lithoprobe data we infer that we imaged the feathering ends of the sill intrusions such sills represent a net addition of crustal material and may provide insight into the ancient stress field during emplacement and clues as to how cratons achieve their thickness and stability although the survey area is small this study represents the first attempt in north america and only the second in the world to examine upper middle crustal structure to depths of approximately 20 km using industry style 3 d seismic reflection data the results indicate that industry 3 d data with extended recording times could provide useful information for studying the crystalline crust below sedimentary basins

uranium lead ages for lunar zircons evidence for a prolonged period of granophyre formation from 4 32 to 3 88 ga the ages of a number of small fragments of lunar granophyre have been determined by the in situ u th pb isotopic analysis of zircon using a sensitive high mass resolution ion microprobe shrimp i the zircon from lunar granophyre is characterized by consistently high u and th contents most 200 500 ppm and 100 300 ppm respectively compared to zircon from mafic lunar rocks some fragments of lunar granophyre are found to be as old as 4 32 ga supporting other evidence that the original lunar magma ocean crystallized completely within 200 ma of the formation of the moon itself other fragments are as young as 3 88 ga which is much later than the time of formation of most of the lunar crust the older lunar granophyres have rare earth element ree patterns that are similar to lunar kreep whilst the younger granophyres have bow shaped ree patterns that feature a greater relative enrichment in the heavy ree the wide range of ages of numerous lunar zircons lunar granophyres and other rocks indicates that zircon forming magmatism in the lunar highlands was most active prior to 4 3 ga but continuous until at least 3 88 ga the u pb isotopic composition of much lunar zircon is near concordant but the effects of isotopic disturbance as late as 1 0 ga are observed in some zircon both within granophyre fragments recrystallized by reheating and within fragments in which the original delicate silica k feldspar granophyric intergrowth is well preserved it is therefore essential to make multiple analyses of individual zircon grains and preferably analyses of suites of zircons from lunar igneous rocks if they are to be dated reliably by the u pb method it is possible that some of the younger lunar granophyres are the product of large scale silicate liquid immiscibility within late stage differentiates but this remains unproven until remnants of demonstrably cogenetic fe rich immiscible liquid are positively identified

transport of indicator clasts by ice sheets and the transport half distance a contribution to prospecting for ore deposits the abundance a of granitic and metamorphic clasts in wisconsinan till in the dummer moraine at the edge of the precambrian shield of ontario decreases exponentially but then remains nearly constant at about 4 for more than 800 km down ice in southwestern ontario ohio and indiana the exponential decrease is attributed to the transport and deposition in the basal ice of the laurentide ice sheet after it crossed the contact between the granitic rocks of the precambrian shield and the overlying paleozoic carbonate rocks the transition from exponential to linear distribution was caused by a change in transport mechanism from basal to englacial transport of clasts that were moved above the base of the ice sheet and thus escaped attrition and deposition in basal till the transport half distance of a boulder train can be estimated from a plot of in a vs transport distance within the exponential transport regime the half distance can then be used to determine the transition distance which indicates how

crustal structure of central japan and its petrological implications the crustal structure of central honshu japan has been influenced by several tectonic events a series of collision processes during the late tertiary extensive faulting highly compressive deformation and quaternary volcanism the southern part of the study area is covered by various granitic rocks which intrude into old palaeozoic formations quaternary volcanoes occupy the northern part and cover the basement which is mainly composed of granitic rocks and tertiary formations a traveltime inversion for velocity and interface depth was applied to the seismic data together with constraints from amplitude forward modelling to produce a seismic velocity model of the crust in central honshu in this experiment both refracted p and s waves are clearly recorded along a 110 km profile these provide constraints on the 2 d p and s wave velocity structure down to a depth of about 10 km moreover clear p wave reflections from intracrustal interfaces provide constraints on deeper parts of the crust down to about 25 km for the p wave velocity model the velocities of near surface layers show large lateral variations from 3 7 to 4 4 km s 1 increasing towards the south underlying layers have velocities ranging from 4 85 to 5 6 km s 1 velocities in the range 5 85 6 2 km s 1 characterize the upper crust that extends to a depth of about 15 km for the s wave velocity model the near surface layer velocities change from 1 7 to 2 55 km s 1 showing remarkable lateral heterogeneity whilst the upper crust is characterized by velocities of 3 4 3 6 km s 1 the deeper parts are modelled by two prominent reflectors in the mid crust the shallower one which delineates the bottom of the upper crust dips southwards from 14 to 16 km the deeper reflector lies between 20 and 24 km depth and dips northwards the velocity in this mid crustal layer is 6 35 km s 1 at the top and 6 7 km s 1 at the bottom the crustal thickness under the profile could not be determined because of a lack of pn and or pm p phases this study also presents the vp vs ratio and the poisson s ratio distribution and gives the probable composition of the upper crust poisson s ratio varies from 0 29 to 0 34 which can be ascribed to a porous and water saturated structure for the near surface layers in the northern part of the region poisson s ratios of about 0 24 0 25 in the southern part and 0 22 0 24 in the upper crust together with the geological data show that the upper crust has a felsic content and is formed by granite granodioritic rocks with a high quartz content the changes in the quartz content explain the lateral variations of vp vs and poisson s ratio in the model the higher velocities in the middle crust suggest a more mafic structure probably composed of diorites

petrology and geochemistry of patuxent range 91501 a clast poor impact melt from the l chondrite parent body and lewis cliff 88663 an l7 chondrite we have performed petrologic and geochemical studies of patuxent range pat 91501 and lewis cliff lew 88663 pat 91501 originally classified as an l7 chondrite is rather a unique near total impact melt from the l chondrite parent body lewis cliff 88663 was originally classified as an achondrite but we find that it is a very weakly shocked l7 chondrite pat 91501 is an unshocked homogeneous igneous textured ultramafic rock composed of euhedral to subhedral olivine low ca pyroxene augite and chrome rich spinels with interstitial albitic plagioclase and minor silica alumina alkali rich glass only 10 relic chondritic material is present olivine grains are homogeneous fa25 2 26 8 low ca pyroxene wo1 9 7 2en71 9 78 2fs19 9 20 9 and augite wo29 8 39 0en49 2 55 3fs11 8 14 9 display a strong linear tio2 al2o3 correlation resulting from igneous fractionation plagioclase is variable in composition or3 0 7 7ab79 8 84 1an8 2 17 2 chrome rich spinels are variable in composition and zoned from cr rich cores to ti al rich rims some have evolved compositions with up to 7 9 wt tio2 pat 91501 bulk silicate has an l chondrite lithophile element composition except for depletions in zn and br siderophile and chalcophile elements are highly depleted due to sequestration in centimeter size metal troilite nodules the minerals in lew 88663 are more uniform in composition than those in pat 91501 olivine grains have low cao and cr2o3 contents similar to those in l5 6 chondrites pyroxenes have high tio2 contents with only a diffuse tio2 al2o3 correlation low ca pyroxenes are less calcic wo1 6 3 1en76 5 77 0fs20 4 21 4 while augites wo39 5 45 6en46 8 51 1fs7 6 9 4 and plagioclases or2 6 5 7ab74 1 83 1an11 2 23 3 are more calcic spinels are homogeneous and compositionally similar to those in l6 chondrites lew 88663 has an l chondrite bulk composition for lithophile elements and only slight depletions in siderophile and chalcophile elements that are plausibly due to weathering and or sample heterogeneity