new insights on the tectonics along the new hebrides subduction zone based on gps results 1 at the new hebrides nh subduction zone ridges born by the subducting australia plate enter the trench and collide with the overriding margin results from gps surveys conducted on both sides of the trench and new bathymetry maps of the nh archipelago bring new light on the complex tectonics of this area convergence vectors present large variations that are not explained by australia pacific a p poles and that define four segments vectors remain mostly perpendicular to the trench and parallel to the earthquake slip vectors slow convergence i e 30 40 mm yr is found at the central segment facing the d entrecasteaux ridge the southern segment moves faster than a p motion predicts 89 to 124 mm yr relatively to a western north fiji basin wnfb reference the northern and southern segments rotate in opposite directions consistently with the extension observed in the troughs east of both segments both rotations combine in central vanuatu into an eastward translation that bulldozes the central segment into the wnfb at 55 mm yr that model suggests that the motion of the central segment forced by the subduction collision of the d entrecasteaux ridge influences the motion of the adjoining segments the new caledonia archipelago is motionless with respect to the rest of the australia plate despite the incipient interaction between the loyalty ridge and the nh margin southeast of the interaction area convergence is partitioned into a 50 mm yr trench normal component accommodated at the trench and a 90 mm yr trench parallel component close to the a p convergence and presumably accommodated by a transform boundary at the rear of the nh arc

plate coupling in the northern south island and southernmost north island new zealand as illuminated by earthquake focal mechanisms subduction of the pacific plate in the northern south island and southernmost north island of new zealand is transitional insofar as the crustal thickness of the pacific plate increases significantly along strike in the northern south island focal mechanisms of 145 events shallower than 100 km in this region have been determined using both first motion polarity data and amplitudes of seismogram envelopes the stress regime in the subducted plate appears to be dominated by slab pull t axes in both the upper and lower planes of the dipping seismic zone generally parallel the local dip of the zone and the average azimuth of these t axes is rotated some 25 clockwise out of the direction of dip of the subducted plate this can be related to the asymmetrical shape of the subducted slab in contrast the stress regime in the overlying plate appears to be dominated by subhorizontal compression low angle thrust events near the plate interface in cook strait and the southernmost north island concentrate in two areas which may mark the updip and downdip edges of a locked region identified from global positioning system gps observations an absence of low angle thrust events near the plate interface in the northern south island and the tendency of p axes of events in the subducted plate to become more horizontal suggest that plate coupling there is stronger than in the southernmost north island differential coupling at the plate interface provides a viable mechanism for producing the large tectonic rotations seen in the northern south island

petrology and chemistry of the new shergottite dar al gani 476 in 1998 dar al gani dag 476 was found in the libyan desert the meteorite is classified as a basaltic shergottite and is only the 13th martian meteorite known to date it has a porphyritic texture consisting of a fine grained groundmass and larger olivines the groundmass consists of pyroxene and feldspathic glass minor phases are oxides and sulfides as well as phosphates the presence of olivine orthopyroxene and chromite is a feature that dag 476 has in common with lithology a of elephant moraine eet a79001 however in dag 476 these phases appear to be early phenocrysts rather than xenocrysts shock features such as twinning mosaicism and impact melt pockets are ubiquitous terrestrial weathering was severe and led to formation of carbonate veins following grain boundaries and cracks with a molar mgo mgo feo of 0 68 dag 476 is the most magnesian member among the basaltic shergottites compositions of augite and pigeonite and some of the bulk element concentrations are intermediate between those of lherzolitic and basaltic shergottites however major elements such as fe and ti as well as lree concentrations are considerably lower than in other shergottites noble gas concentrations are low and dominated by the mantle component previously found in chassigny a component similar to that representing martian atmosphere is virtually absent the ejection age of 1 35 0 10 ma is older than that of eeta79001 and could possibly mark a distinct ejection dar al gani 476 is classified as a basaltic shergottite based on its mineralogy it has a fine grained groundmass consisting of clinopyroxene pigeonite and augite feldspathic glass and chromite ti chromite ilmenite sulfides and whitlockite isolated olivine and single chromite grains occur in the groundmass orthopyroxene forms cores of some pigeonite grains shock features such as shock twinning mosaicism cracks and impact melt pockets are abundant severe weathering in the sahara led to significant formation of carbonate veins crosscutting the entire meteorite dar al gani 476 is distinct from other known shergottites chemically it is the most magnesian member among known basaltic shergottites and intermediate in composition for most trace and major elements between iherzolitic and basaltic shergottites unique are the very low bulk ree element abundances the ci normalized abundances of lrees are even lower than those of iherzolitic shergottites the overall abundance pattern however is similar to that of que 94201 textural evidence indicates that orthopyroxene as well as olivine and chromite crystallized as phenocrysts from a magma similar in composition to that of bulk dag 476 whether such a magma composition can be a shergottite parent melt or was formed by impact melting needs to be explored further at this time it cannot entirely be ruled out that these phases represent relics of disaggregated xenoliths that were incorporated and partially assimilated by a basaltic melt although the texture does not support this possibility trapped noble gas concentrations are low and dominated by a chassigny like mantle component virtually no martian atmosphere was trapped in dag 476 whole rock splits the exposure age of 1 26 0 09 ma is younger than that of most shergottites and closer to that of eeta79001 the ejection age of 1 35 0 1 ma could mark another distinct impact event

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

global geodesy using gps without fiducial sites baseline lengths and geocentric radii have been determined from gps data without the use of fiducial sites data from the first gps experiment for the iers and geodynamics gig 91 have been analyzed with a no fiducial strategy a baseline length daily repeatability of 2 mm 4 parts per billion was obtained for baselines in the northern hemisphere comparison of baseline lengths from gps and the global vlbi solution glb659 caprette et al 1990 show rms agreement of 2 1 parts per billion the geocentric radius mean daily repeatability for all sites was 15 cm comparison of geocentric radii from gps and sv5 murray et al 1990 show rms agreement of 3 8 cm given n globally distributed stations the n n 1 2 baseline lengths and n geocentric radii uniquely define a rigid closed polyhedron with a well defined center of mass geodetic information can be obtained by examining the structure of the polyhedron and its change with time

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

tectonic motion and deformation from satellite laser ranging to lageos satellite laser ranging slr to lageos acquired during the period 1978 1988 has been analyzed to yield estimates of tectonic motion for 22 laser tracking stations situated on seven major plates the analysis is based on the precise modeling of the orbit dynamics of lageos and includes the determination of other geodynamic and nonconservative force model parameters involved in the orbit determination problem at the centimeter level site velocities were recovered from station positions determined each calendar quarter using a network adjustment procedure which maintains the reference frame within the stable interior of tectonic plates the recovered motions indicate good agreement with existing estimates of stress fields particularly across northern europe the eastern pacific and in the basin and range province of north america a comparison of the intersite motions for stations centrally located on separate plates between slr and those implied by the nuvel 1 geologic motion model yield a strong positive correlation of 0 989 and a 3 7 scale difference which may be attributable to recent changes in relative velocities or geologic time scale uncertainties sites located at or within 250 km of convergent plate boundaries have additional components of motion indicating a need for further tectonic modeling beyond that provided by simple rigid plate motions for lines crossing the north atlantic the san andreas fault and within the basin and range province the geodesic rates determined by slr are in good agreement with those determined by very long baseline interferometry an alternative space geodetic technique

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

insights into martian water reservoirs from analyses of martian meteorite que94201 the martian atmospheric d h value of 5 2 times terrestrial is significantly higher than any found on earth and has been ascribed to preferential loss of h relative to d from the atmosphere through jeans escape over time here based on ion microprobe analyses of apatite grains from martian meteorite que94201 it is shown that the pre jeans escape martian water reservoir has a d h value twice that of terrestrial water rather than the terrestrial value that has been assumed in prior work the data support a two stage history for martian volatiles in which early hydrodynamic escape enriched martian water to 2x terrestrial d h values subsequent jeans escape to produce the current atmospheric values has thus been responsible for less d enrichment than previously thought a martian crust containing 2 3 times more water than previously proposed is implied by the results

petrogenesis of shergottite meteorites inferred from minor and trace element microdistributions abstract as an extension of our previous work on the lherzolitic shergottites alha77005 and lew88516 ion microprobe measurements of rees and other selected trace and minor elements were made in individual minerals of the basaltic shergottites shergotty zagami and eeta79001 whole rock ree abundances in these achondrites are dominated by whitlockite which is usually present only in trace amounts one of the most significant features is the extensive zoning of trace and minor elements in pyroxenes this zonation which provides information on the crystallization histories of these meteorites is of primary magmatic origin and not the result of secondary processes such as diffusive reequilibration and or metasomatic infiltration coherent trends in element element plots for low ca pyroxenes indicate that each shergottite formed essentially by progressive closed system fractional crystallization the calculated ree patterns of the parent melts of all shergottites are lree depleted and parallel to their whole rock ree patterns also indicative of closed system fractional crystallization on the basis of observations reported in this study as well as previously determined petrologic and geochemical including isotopic characteristics we present a model that suggests possible relationships among all five known shergottites

los angeles the most differentiated basaltic martian meteorite los angeles is a new martian meteorite that expands the compositional range of basaltic shergottites compared to shergotty zagami que94201 and eet79001 b los angeles is more differentiated with higher concentrations of incompatible elements e g la and a higher abundance of late stage phases such as phosphates and k rich feldspathic glass the pyroxene crystallization trend starts at compositions more ferroan than in other martian basalts trace elements indicate a greater similarity to shergotty and zagami than to que94201 or eet79001 b but the mg fe ratio is low even compared to postulated parent melts of shergotty and zagami pyroxene in los angeles has 0 7 4 m thick exsolution lamellae 10 times thicker than those in shergotty and zagami opaque oxide compositions suggest a low equilibration temperature at an oxygen fugacity near the fayalite magnetite quartz buffer los angeles cooled more slowly than shergotty and zagami slow cooling coupled with the ferroan bulk composition produced abundant fine grained intergrowths of fayalite hedenbergite and silica by the breakdown of pyroxferroite shock effects in los angeles include maskelynitized plagioclase pyroxene with mosaic extinction and rare fault zones one such fault ruptured a previously decomposed zone of pyroxferroite although highly differentiated the bulk composition of los angeles is not close to the low ca si composition of the globally wind stirred soil of mars

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

que94201 shergottite crystallization of a martian basaltic magma abstract basaltic shergottites are commonly described as having crystallized from magmas that contained entrained or cumulus pyroxenes complexly zoned clinopyroxenes in que94201 a newly recovered antarctic shergottite are similar to those formed during continuous growth in some lunar basaltic melts pyroxene cores have nuclei of magnesian pigeonite mantled by augite in turn rimmed by strongly zoned ferroan pigeonite with outer rims of pyroxferroite fe ti oxide compositions indicate that this meteorite crystallized under relatively reducing conditions more like lunar basalts than other shergottites ree and other trace element abundances in zoned pyroxenes maskelynite and phosphates are consistent with continuous pyroxene crystallization from an evolving magma punctuated by the appearance of new phases on the liquidus the higher proportion of maskelynite in que94201 suggests that its composition may be closer to multiple saturation with pyroxenes plagioclase than other shergottites and all pyroxene zones show negative eu anomalies thus this meteorite may represent the first example of a martian magma unaffected by crystal accumulation the fe fe mg ratio and proportions of incompatible elements reflected in 4 modal whitlockite are high implying that this is a fractionated melt the calculated bulk ree pattern shows extreme lree depletion suggesting either less contamination with enriched crustal materials or a more lree depleted source than other basaltic shergottites

mars regolith versus snc meteorites possible evidence for abundant crustal carbonates abstract viking xrf analyses of the martian regolith are compared with typical igneous rocks of the earth the moon the eucrite parent asteroid and especially the shergottites nakhlites and chassigny snc meteorites which are suspected to be basalts and mafic cumulates from mars a striking feature of the martian regolith compared to igneous rocks with similar molar mg fe si ratios is its extraordinarily low ca si ratio the regolith s low ca si ratio is probably not a result of simple mixing isochemical weathering of snc like rocks with other igneous rocks unless the regolith contains a large component of rock with an improbable combination of extremely low ca si and mg fe si and yet low k 2 o and zr several other models might conceivably account for the low ca si ratio but i suggest that most of the missing ca was removed from the regolith as ca carbonate formation of a mass of carbonate equivalent to a global shell 20 m thick would suffice to remove 1000 mbar of co 2 from the martian atmosphere thus the peculiar ca si ratio of the martian regolith tends to support the hypothesis that the climate of mars was once far warmer and wetter than it is today

late quaternary slip rates and slip partitioning on the alpine fault new zealand abstract published geological data on late quaternary offsets on the alpine fault new zealand have been assembled into a common format and analysed with respect to uncertainties uncertainties arise mainly from measurement of offset features relating apparent offsets to actual fault slip and dating the offset features despite the considerable uncertainties the data form a coherent set consistent with a relatively constant rate of strike slip of 27 5 mm year between milford sound and hokitika this rate represents 70 75 of the fault parallel interplate motion north of the confluence with the hope fault the rate drops substantially dip slip rates on the other hand show considerable variation along strike rising to a maximum of more than 10 mm year in the central section and decreasing to zero at the southern end partitioning of c 25 of the interplate slip on to structures east of the alpine fault occurs in the central section consistent with predictions from critical wedge models the partitioning of all the fault normal component of displacement on to other structures in the south may be related in part to a doubling in width of the deforming wedge to the east most probably however the fault normal displacement is mainly accommodated by underthrusting of the australian plate offshore due to a change in the nature of the crust from continental to oceanic

re evaluation of intercumulus liquid composition and oxidation state for the shergotty meteorite abstract the shergotty martian meteorite contains pigeonite and augite with homogeneous magnesian cores thought to be cumulus crystals using elemental maps of thin sections we estimate the abundance of cumulus pyroxene cores at 13 vol this estimate is roughly half that determined from prior melting experiments 28 and coincides with the observation of a similar discrepancy between the proportions of cumulus pyroxenes estimated from modal observations and melting experiments in the zagami shergottite an intercumulus liquid composition calculated using this new cumulus pyroxene estimate is virtually identical to that calculated for zagami our results suggest the possibility that melting experiments may not have been carried out under conditions appropriate for crystallization of the shergottites we consider two possible explanations crystallization of pyroxene cores at depth or under different redox conditions prior arguments for polybaric crystallization of shergottites based on pyroxene intergrowths and kaersutite inclusions are inconclusive using the melts program we have explored crystallization at higher pressure a greater proportion of pyroxene crystallizes at higher pressures rather than a smaller amount as necessary in this model even in calculations at 1 bar pigeonite crystallizes before augite and the temperature interval between the appearance of pigeonite and augite expands with pressure both pigeonite and augite appear to be in equilibrium with the same liquid composition and thus are thought to have co crystallized in shergotty so it seems likely that melts may not correctly predict pyroxene crystallization behavior in this fe rich magma fe ti oxide compositions in shergotty were previously used as evidence that the magma crystallized at redox conditions near qfm however ghosal et al 1998 recently suggested that the oxides record subsolidus reducing conditions of qfm 3 at 602 c and our analyses support that conclusion if a new solution model for oxides is used they also proposed that fe3 in shergotty pyroxenes indicates magmatic crystallization at approximately qfm 3 and our estimates of fe3 calculated from pyroxene stoichiometry in microprobe analyses match their reported values however we doubt that stoichiometric calculations provide accurate fe3 determinations other indicators suggest that magmatic conditions were oxidizing the feo content of shergotty maskelynite is greater and the negative eu anomaly in pyroxene cores is shallower than in another basaltic shergottite que94201 which is thought to have crystallized under reducing conditions near qfm 4 also the presence of silica fayalite and magnetite in mesostasis indicates oxiding conditions at least at a late magmatic stage thus we argue that shergotty crystallized under redox conditions near qfm

continuous growth of hydrogenetic ferromanganese crusts since 17 myr ago on takuyo daigo seamount nw pacific at water depths of 800 5500 m ferromanganese crusts cover all outcrops on takuyo daigo seamount traversed during remotely operated underwater vehicle rov dives except in places covered by foraminifera sand takuyo daigo is a cretaceous seamount located in the northwest pacific ocean geological and bathymetric mapping provide the framework for this study chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths even through the modern oxygen minimum zone omz contrary to some earlier models for deposition growth rates vary from 2 3 to 3 5 mm myr with fe or mn fluxes of 0 07 0 11 g cm2 myr since the early middle miocene co mn ratios decrease with water depth while fe mn and other metallic elements increase or show no change based on the analysis of the uppermost crust surface this is probably because co is the most abundant redox sensitive element derived from seawater that occurs in crusts

transpressive ductile flow and oblique ramping of lower crust in a two sided orogen insight from quartz grain shape fabrics near the alpine fault new zealand 1 the three dimensional 3 d grain shape fabric gsf of deformed quartz veins was measured in 30 samples from the hanging wall of the oblique slip alpine fault in the central southern alps new zealand these record aspects of the neotectonic strain experienced by lower crustal rocks in the pacific plate as they were transported through a two sided orogen deformation was nonsteady state transpression was followed by near vertical shearing as the rocks negotiated the oblique footwall ramp of the alpine fault at the brittle ductile transition ramping up was accommodated by an escalator like back shearing process this thinned the transpressed crust and boosted dip slip rate on the alpine fault mechanically this suggests a sharp step in the footwall ramp adjacent to which differential stresses were transiently high margin parallel motion was partitioned onto these shears fabric development is simulated using a 3 d kinematic model into which we input constraints on plate motion fault slip rates crustal structure fabrics and geodetic strain in the southern alps this model can explain many aspects of the southern alps fabrics including their nonvertical foliation and lineation similarities between the model predictions and the observed fabrics suggest that lower crustal flow in the pacific plate mimicked the geodetic velocity pattern at the surface today with obliquely convergent deformation being distributed across a wide region to the east of the alpine fault the model shows that the timescale for an exhumational steady state with respect to deformational fabrics is slow 107 years a condition which the 6 m y old southern alps have probably not yet achieved

north america pacific plate boundary an elastic plastic megashear evidence from very long baseline interferometry i investigate a number of lithospheric deformation models based upon the concept that the motions of points near the north america pacific plate boundary are a linear combination of north america and pacific velocities this concept entails a shear strain transition zone in the vicinity of the boundary the best of these models fit 95 of the variance in 139 very long baseline interferometry vlbi length and transverse velocity observations taken over 5 5 years and require only 90 of the relative plate motion predicted by rm2 residual misfits in the megashear models are largely explained by a 6 1 mm yr component of basin and range spreading perpendicular to the plate boundary instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the san andreas fault some of this deformation will be recovered through elastic rebound the rest will be permanently set through plastic processes thus depending on the elastic plastic composition of the borderlands the width and pattern of strain accumulation in the megashear over geological time may or may not be significantly different than what is currently observed because vlbi data have been assembled for only a small fraction of the earthquake cycle plastic and elastic strains are indistinguishable other information will have to be brought to bear to discriminate elastic and plastic behaviors and reconcile instantaneous and geologic deformation near the north america pacific margin

geodesy by radio interferometry evidence for contemporary plate motion analysis of 211 very long baseline interferometry observing sessions carried out between november 1979 and august 1984 has yielded estimates of the distances between various radio telescopes located in north america and europe the average rate of change of the distances between four radio telescopes in north america haystack observatory massachusetts westford radio telescope massachusetts george r agassiz station texas and owens valley radio observatory california and one in europe onsala space observatory sweden obtained from the analysis of these data is 19 10 mm yr where the 68 confidence interval standard deviation is for the estimate of the rate of change of the haystack onsala baseline length the one determined most accurately from these data this estimate of the standard deviation is dominated by the effects of correlated systematic errors due mostly to errors in the model used for the atmospheric delay which we infer introduces errors in each baseline length estimate of 40 mm standard deviation and 60 days correlation time by contrast the statistical standard deviation is only 2 mm yr the estimated geologic rates of change of these baseline lengths averaged over 106 years are 15 to 17 3 mm yr for the various north american sites to onsala improvements in our model of the atmosphere and continued monitoring of the distances between north american and european telescopes will allow the uncertainty of the rate estimates to be reduced over the next few years to a value small compared to our estimated rate of change of these baseline lengths the use of multiple radio telescopes in europe will allow us also to separate possible local site motions from plate motions

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

large scale tectonic plate motions measured with the doris space geodesy system we have analysed approximately 3 years of doppler tracking measurements of the doris system on the spot2 and topex poseidon satellites absolute velocities of 19 stations of the doris network have been computed through a dynamic orbit computation method these stations are located on 9 major tectonic plates for 14 stations relative velocities across 28 plate boundaries involving 8 different plates agree quite well with the nuvel 1 geological estimates with a correlation coefficient of 0 982 and a slope of 1 00 0 02 this study provides the first space geodesy derived motion of the african plate which is based on data taken at 4 stations computed rotation vectors for the relative motions between the eurasian pacific and african plates show a good agreement with nuvel 1 vectors for the remaining sites which are typically located close to plate boundaries measured motions depart significantly from the ones predicted by nuvel 1 the site of fairbanks alaska appears to move anomalously compared to earlier vlbi results

new constraints on seismicity in the wellington region of new zealand from relocated earthquake hypocentres summary the wellington region of new zealand overlies a strongly coupled portion of the shallow subduction interface between the pacific and australian plates to better understand the active deformation in the area we perform a double difference dd relocation of 6825 local earthquakes that occurred between 1990 and 2001 using both cross correlation cc and bispectrum bs methods we calculate high quality waveform based differential times wbdts for event pairs we manage to more than triple the s wave differential time measurements after reasonably estimating many of the unpicked s arrivals after relocation the image of the double seismic zone beneath this region is greatly sharpened we find several northeast striking linear seismic features near lake wairarapa on the north island which may result from slip along normal faults within the subducting pacific plate we further search for repeating events that might define creeping patches along the interplate thrust using a 20 s data window for cc we find 287 event clusters with very high waveform similarities most of these clusters contain just a doublet that occurred within a short time period the failure to find repeating earthquakes along the plate boundary in this 12 yr time period is consistent with the hypothesized strong coupling between the pacific and australian plates under the wellington region

observing tectonic plate motions and deformations from satellite laser ranging for the first time satellite laser ranging slr measurements from lageos are revealing changes in geodetic station positions suggestive of predicted global tectonic plate motions a detailed discussion of the latest slr results is given herein since the accuracy of tectonic plate velocities increases with the repetition rate and accuracy in the measurement of interplate distances activities are also described for increasing the temporal resolution and precision of baseline determinations the lageos laser data for the period january 1979 to the end of 1982 have been reanalyzed the results of this analysis are now approaching the useful accuracies required by geophysics for the better annually determined stations they include consistencies of 2 3 cm in station heights and 2 cm in annual baselines the slr results show overall agreement with the geologic tectonic rate model of minster and jordan with a linear cross correlation of 0 61 for 34 observed interstation rates improved temporal resolution was obtained in the measurement of specific baselines of moderate length through the large number of simultaneously observed passes

present day tectonic plate motions and crustal deformations from the doris space system doppler orbitography and radiopositioning integrated by satellite doris data acquired between january 1993 and december 1996 from the spot 2 spot 3 and topex poseidon satellites have been analyzed to determine velocities for 45 sites on eight major tectonic plates for 28 sites far from deformation zones the velocity estimates agree with plate model predictions least squares computation of poles of rotation which model the plate motions shows that for eurasia africa pacific and south america plates the agreement is better with nuvel 1 while for australia antarctica nazca and north america plates the doris euler vectors are closer to ntjvel 1a in general doris results do not differ significantly from other space geodetic techniques determinations but provide better estimates for plates poorly or inhomogeneously covered by global positioning system gps very long baseline interferometry vlbi and satellite laser ranging slr networks such as africa the doris coverage of this plate allows discussion of intraplate deformations due to the motion of the eastern africa part which constitues the somalia plate sites located in deformation zones such as western eurasia boundaries central asia southwestern america coast south east asia show motion with respect to their own plates comparisons with other geodetic measurements for colocated stations or with regional geodynamical models show the interest of doris in active zones where global plate models are not valid

global positioning system measurements of indian plate motion and convergence across the lesser himalaya we use global positioning system gps measurements acquired from 1991 to 1995 to constrain the motion of sites in bangalore in southern india and kathmandu nepal relative to a global gps network these measurements permit estimates of the northward motion of the indian plate and convergence between the southern himalaya and the indian subcontinent the velocities of bangalore and kathmandu in the itrf92 reference frame agrees with that predicted by the nnr nuvel1a plate motion model for indian plate motion and differ from that predicted for the australian plate confirming the independent motion of the indian and australian plate fragments no significant motion was detected between bangalore and kathmandu during the three years from 1991 1994 even though kathmandu is located in the hanging wall of the active himalayan thrust system the himalayan thrust system is thought to accommodate 18 7 mm yr of convergence and has been the source of several historic m 8 earthquakes the absence of motion of kathmandu relative to the indian plate can be explained if the thrust system is presently locked south of the greater himalaya our preferred model has no steady slip on the detachment south of the greater himalaya and steady slip at a rate greater than 6 mm yr 1 3 of the long term convergence rate can be ruled out at 95 confidence level

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

relative motions of the australian pacific and antarctic plates estimated by the global positioning system gps measurements spanning 3 years have been used to determine velocities for 7 sites on the australian pacific and antarctic plates the site velocities agree with both plate model predictions and other space geodetic techniques we find no evidence for internal deformation of the interior of the australian plate wellington new zealand located in the australian pacific plate boundary zone moves 20 5 mm yr west southwest relative to the australian plate its velocity lies midway between the predicted velocities of the two plates relative euler vectors for the australia antarctica and pacific antarctica plates agree within one standard deviation with the nuvel 1a predictions

crustal deformation of the marlborough fault zone in the south island of new zealand geodetic constraints over the interval 1982 1994 crustal deformation across the marlborough fault zone in the south island of new zealand has been investigated by resurveying with the global positioning system gps a triangulation and trilateration network across part of the zone the principal strain rates which mostly have errors between 5 and 10 vary systematically across the region the principal axis of horizontal contraction gradually swings from se nw southeast of the hope fault to almost east west in the west the component of velocity parallel to the strike of the faults can account for 95 of the relative motion between the australian and pacific plates this component exhibits little variation west of the alpine wairau fault and shows an almost linear variation from the wairau fault to the east coast the horizontal strain rate northwest of the wairau fault is a small east west uniaxial contraction 0 1 ppm yr 1 if it is assumed that the crustal blocks bounded by the major faults are primarily driven by basal shear tractions with stresses on the faults being relatively insignificant then the slip rates expected on the faults may be derived from the observed velocity variations across the fault zone these predicted slip rates are in good agreement with geologically observed slip rates the larger slip rates on the hope fault are related to the observation that the strain field extends southeast of the fault over a distance large compared with the spacing between the faults the agreement between predicted and geological slip rates lends support to the idea that the observed pattern of deformation reflects that in the lower lithosphere

zagami product of a two stage magmatic history abstract large specimens of the zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths we document the presence of whitlockite and of melt veins and pockets of shock origin pyroxene crystals have homogeneous mg rich pigeonite and augite cores overgrown by fe rich zoned pyroxene mostly pigeonite rims amphibole bearing magmatic melt inclusions occur exclusively in the cores we conclude that zagami experienced a twostage crystallization history the first stage occurred in a deep seated slowly cooling magma chamber there the homogeneous mg rich cores of the pyroxenes crystallized during relatively slow cooling the deep seated origin of the cores is also indicated by the presence of amphibole within them which requires pressures of formation equivalent to crystallization at depths 7 5 km on mars modest abundance of homogeneous mg rich cores 15 20 indicates that crystal settling did not play a significant role in this part of the magma chamber during the second stage the mg rich pyroxenes were entrained into a magma that either intruded to the near surface and cooled in a relatively thin dike or sill or extruded to the surface and crystallized in a lava flow 10 m thick again without indications for crystal settling this scenario is suggested by estimates of cooling rates of 0 1 0 5 c h based on sizes of the plagioclase maskelynite crystals and of 0 02 c h based on the width of pyroxene exsolution lamellae brearley 1991 irregular shapes of the mg rich cores result from resorption and possible solid state diffusion and the shapes and sizes of the pyroxenes after crystallization of fe rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores the finer grained areas of the rock inherited smaller and more numerous mg rich pyroxene cores from the first stage than did the coarser grained areas crystallization of both augite and pigeonite cores at depth but mostly pigeonite rims in the nearsurface environment may be the result of a phase boundary shift and expansion of the pigeonite stability field at lower pressures the estimated depth of the magma chamber for zagami of 7 5 km and thickness of the putative lava flow of 10 m are consistent with calculations and observations of volcanic constructs and flows in the tharsis region of mars

origin of planetary cores evidence from highly siderophile elements in martian meteorites we present new bulk compositional data for 6 martian meteorites including highly siderophile elements ni re os ir and au these and literature data are utilized for comparison versus the siderophile systematics of igneous rocks from earth the moon and the hed asteroid the siderophile composition of alh84001 is clearly anomalous whether this reflects a more reducing environment on primordial mars when this ancient rock first crystallized or secondary alteration is unclear que94201 shows remarkable similarity with eet79001 b for siderophile as well as lithophile elements both are extraordinarily depleted in the noblest siderophiles os and ir to roughly 0 00001 ci chondrites as in terrestrial igneous rocks among martian rocks ni os and ir show strong correlations vs mgo in the case of mgo vs ni the martian trend is displaced toward lower ni by a large factor 5 but the os and ir trends are not significantly displaced from their terrestrial counterparts for mars re shows a rough correlation with mgo indicating compatible behavior in contrast to its mildly incompatible behavior on earth among martian mgo rich rocks au shows a weak anticorrelation vs mgo resembling the terrestrial distribution except for a displacement toward 2 3 times lower au the same elements ni re os ir and au show similar correlations with cr substituted for mgo data for lunar and hed rocks generally show less clear cut trends relatively few mgo rich samples are available these trends are exploited to infer the compositions of the primitive earth mars moon and hed mantles by assuming that the trend intercepts the bulk mgo or cr content of the primitive mantle at the approximate primitive mantle concentration of the siderophile element results for earth show good agreement with earlier estimates for mars the implied primitive mantle composition is remarkably similar to the earth s except for 5 times lower ni the best constrained of the extremely siderophile elements os and ir are present in the martian mantle at 0 005 times ci in comparison to 0 007 times ci in earth s mantle this similarity constitutes a key constraint on the style of core mantle differentiation in both mars and earth successful models should predict similarly high concentrations of noble siderophile elements in both the martian and terrestrial mantles high compared to the lunar and hed mantles and to models of simple partitioning at typical low pressure magmatic temperatures but only predict high ni for the earth s mantle models that engender the noble siderophile excess in earth s mantle through a uniquely terrestrial process such as a moon forming giant impact have difficulty explaining the similarity of outcome except for ni on mars the high ni content of the terrestrial mantle is probably an effect traceable to earth s size for the more highly siderophile elements like os and ir the simplest model consistent with available constraints is the veneer hypothesis core mantle differentiation was notably inefficient on the largest terrestrial planets because during the final 1 of accretion these bodies acquired sufficient h2o to oxidize most of the later accreting fe metal thus eliminating the carrier phase for segregation of siderophile elements into the core

gps applications for geodynamics and earthquake studies geodetic measurements obtained with the global positioning system gps are increasingly more widely applied in geophysical studies in this paper we review the changes to the technology of gps geodesy over the last five years that are responsible for this increased applicability we survey geophysical investigations employing gps to measure coseismic postseismic and interseismic deformation plate motion and crustal deformation at plate boundaries volcano deformation and the deformation associated with glacial isostatic adjustment and its application to sea level studies we emphasize the use of gps determinations for the modeling of this wide variety of geophysical phenomena we also discuss the recent advent of permanent gps networks for regional geophysical studies as well as the possible future of gps surveying in light of the recent advances

impact melting of the cachari eucrite 3 0 gy ago both the host phase and glass veins of the cachari eucrite have been analyzed by microprobe and neutron activation analysis for their chemical compositions and by mass spectrometry for their 39ar 40ar gas retention ages cachari is chemically similar to other non cumulate eucrites the vesicular glass veins vary from pure glass to devitrified glass to areas that are substantially crystalline the glassy areas have nearly the same concentrations of major and trace elements as the unmelted portions of cachari but some differences probably due to preferential dissolution occur along melt contacts the glass formed by shock melting of cachari host or of rock identical to it 39ar 40ar data for the host and glass suggest distinctly different ages of 3 04 07 gy and 3 47 04 gy respectively the time of glass formation which may also be the time of brecciation is most likely given by the 3 0 gy age of the host the higher age for the glass is interpreted to represent incomplete ar degassing during the 3 0 gy event due to the greater resistance to ar diffusion shown by the glass compared to the host event ages significantly younger than 4 5 gy have now been determined for several eucrites and howardites and suggest a long dynamic regolith history for the parent body

new lithologies in the zagami meteorite evidence for fractional crystallization of a single magma unit on mars abstract zagami consists of a series of increasingly evolved magmatic lithologies the bulk of the rock is a basaltic lithology dominated by pigeonite fs 28 7 54 3 augite fs 19 5 35 0 and maskelynite ab 42 53 approximately 20 vol of zagami is a basaltic lithology containing feo enriched pyroxene pigeonite fs 27 0 80 8 and mm to cm sized late stage melt pockets the melt pockets are highly enriched in olivine bearing intergrowths mesostases phosphates both whitlockite and water bearing apatite fe ti oxides and sulfides the systematic increases in abundances of late stage phases fs and incompatible element e g y and the rees contents of pigeonite ab contents of maskelynite and feo concentrations of whitlockite all point to a fractional crystallization sequence the crystallization order in zagami and the formation of these various lithologies was controlled by the abundances of iron phosphorus and calcium during fractional crystallization iron and phosphorus enrichment occurred ultimately forcing the crystallization of calcium phosphates and olivine bearing intergrowths the limited amount of calcium in the melt and its partitioning between phosphates and silicates controlled the crystallization of phosphates plagioclase pigeonite and augite the presence of these feo enriched water poor late stage lithologies has important implications discrepancies between experimental and petrologic studies to infer the history of basaltic shergottites may be partially explained by the use of starting compositions which are too feo poor in the experimental studies the water poor nature of the late stage melt pockets suggests crystallization from a very dry magma although whether this magma was always dry or experienced significant near surface degassing remains an open question finally the presence of fractional crystallization products within zagami suggests that this may be a relatively common process on mars