sensitivity analysis of drilling parameters in rock rotary drilling process based on orthogonal test method abstract drilling exploration is the main method for geological studies of rocks and soil selecting reasonable drilling parameters is important for ensuring the safety and economic benefits of a project according to the force limit equilibrium of rock during rotary drilling and using the energy equilibrium method the relationship between the vertical drilling efficiency and drilling parameters such as the speed of rotation thrust force and rotation torque were deduced in this study through improvements in the drilling process monitoring dpm system it was possible to quickly efficiently and quantitatively obtain the drilling parameters during rock drilling an in situ drilling test of granite using the improved dpm system showed the sensitivity of the drilling efficiency to each drilling parameter via an orthogonal test the results indicated that the optimal drilling efficiency 13 2 was achieved under the following test conditions a rotation speed of 128 r min thrust force of 788 kpa and a rotation torque of 64 n m the influence of the thrust force on the drilling efficiency was extremely significant the sensitivity of this parameter was high and the weight value of the thrust force had a 57 87 influence among the others furthermore the influence of the rotation torque on the drilling efficiency index was significant the sensitivity to this parameter was neither high nor low and its weight value was 36 82 in contrast the influence of the rotation speed on the index was insignificant sensitivity to this parameter was low and its weight value was 5 31 the research methods and results presented herein can serve as references for the optimum design of drilling construction and the reasonable selection of drilling parameters

direct ion microprobe u pb dating of fossil tooth of a permian shark abstract we report here direct ion microprobe dating of fossil tooth dentine of a permian fresh water shark orthacanthus senckenbergianus using the shrimp instrument recently installed at hiroshima university fifteen spots on the small sample approximately 2 mm 1 mm indicate a 238 u 206 pb isochron age of 266 18 ma and a tera wasserburg concordia intercept age of 266 24 ma in a three dimensional 238 u 206 pb 207 pb 206 pb 204 pb 206 pb diagram these permian ages are consistent with a 235 u 207 pb age of 453 170 ma and a 232 th 208 pb age of 235 310 ma suggesting indistinguishable depositional and early diagenetic ages of the fossil in its sedimentary sequences the success of the method depends on the chemical fractionation of uranium from lead in a specimen a few hundred microns in size and the consequent variations in lead isotopic compositions due to radioactive decay

geometric considerations of the three dimensional u pb data presentation abstract the three dimensional discordia plane is geometrically derived from basic assumptions it is shown that the projections of data which are located on a plane in xyz space onto the three coordinate planes yield different informations the projection from the common lead point yields the discordia line the yz projection the lead lead isochron plot and the xz projection the 206 pb 238 u isochron plot also discussed is the possibility to extend the wetherill discordia plot into three dimensions including the initial lead

chronology and petrogenesis of young achondrites shergotty zagami and alha77005 late magmatism on a geologically active planet a study was undertaken to determine the chronology petrogenesis and relationships among the shergottites shergotty and zagami and the unique achondrite alha77005 these meteorites are the product of a variety of complex processes petrogenesis chondrite normalized abundance patterns of shergotty and zagami are very similar and show pronounced depletions of both the light ree la nd and heavy ree dy lu relative to sm gd these characteristic depletions are even more pronounced for alha77005 the light ree depletion is qualitatively consistent with the presence of cumulus pyroxene and or olivine in these meteorites but trace element models show that the parental magmas of all three meteorites were probably also light ree depleted both trace element model calculations and combined rb sr and sm nd isotopic systematics show that the meteorites could not have been co magmatic nor can alha77005 be representative of the source material of the shergottites light ree depletion of the parental magmas also implies light ree depletion of the source material the sm nd systematics of the shergottites require a time averaged sub chondritic light ree enriched sm nd ratio since 4 6 ae ago the sm nd systematics of alha77005 permit a time averaged super chondritic light ree depleted sm nd ratio if its crystallization age is less than tice 0 72 ae chronology rb sr internal isochrons for all three meteorites and a sm nd internal isochron for zagami are concordant at 180 myr 39ar 40ar plateau ages of shergotty and zagami maskelynite are 250 260 myr these ages apparently reflect resetting of these isotopic systems by shock metamorphism which converted the feldspar to maskelynite the concordance of these ages suggests a single shock event during which the meteorites were in close physical proximity the time of this event is most precisely given by the rb sr age of 180 4 myr for zagami the crystallization ages of the meteorites were not precisely determined extreme upper limits are determined by sm nd model ages relative to an eucrite initial 143nd144nd 0 505835 at 4 6 ae ago these model ages for shergotty zagami and alha77005 are 3600 3500 and 2850 myr respectively the sm nd whole rock age of 1340 60 myr for the three meteorites gives the crystallization age if the sm nd ratios of the precursor materials were always the same we consider this 1340 myr age as a best estimate upper limit best estimate lower limits for shergotty and zagami are taken from the average 39ar 40ar ages of 1200 and 900 myr of pyroxene separates the average 39ar 40ar age of a whole rock sample of alha77005 was 1600 myr and can be partitioned between a low temperature feldspar phase and a high temperature olivine pyroxene inclusions phase the average apparent 39ar 40ar age of the low temperature phase is 1050 myr which is chosen as the best estimate lower limit to the age the crystallization ages of shergotty zagami and alha77005 probably lie within the ranges of 1200 1300 900 1300 and 1000 1300 myr respectively the rb sr whole rock age of 4400 400 myr and single stage babi model ages of 4800 5100 myr are interpreted as reflecting differentiation of the parent body at 4600 myr ago the complex geochemical and isotopic evolution recorded by these meteorites suggests a geologically active parent body capable of sustaining melting at two or more epochs in its history

ion microprobe u th pb dating and ree analyses of phosphates in the nakhlites lafayette and yamato 000593 000749 u th and pb isotopes and rare earth elements rees in individual phosphate grains from martian meteorites lafayette and yamato 000593 000749 were measured using a sensitive highresolution ion microprobe shrimp observed u pb data of 12 apatite grains from yamato y 000593 000749 are well represented by linear regressions in both conventional 2d isochron plots and the 3d u pb plot total pb u isochron indicating that the formation age of this meteorite is 1 53 0 46 ga 2 on the other hand the data of nine apatite grains from lafayette are well represented by planar regression rather than linear regression indicating that its formation age is 1 15 0 34 ga 2 and that a secondary alteration process slightly disturbed its u pb systematics as discussed in the literature regarding nakhla the observed ree abundance patterns of the apatites in lafayette and yamato 000749 normalized to ci chondrites are characterized by a progressive depletion of heavy rees hrees a negative eu anomaly similarity to each other and consistency with previously reported data for nakhla considering the extensive data from other radiometric systems such as sm nd rb sr ar ar and trace elements our results suggest that the parent magmas of the nakhlites including the newly found y 000593 000749 are similar and that their crystallization ages are 1 3 ga

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

u pb and hf isotope study on detrital zircons from the paranoa group brasilia belt brazil constraints on depositional age at mesoproterozoic neoproterozoic transition and tectono magmatic events in the sao francisco craton abstract the eastern portion of the brasilia belt part of the neoproterozoic tocantins province in central brazil is mainly constituted by metasedimentary rocks that partially represent the evolution of a passive margin developed during the meso neoproterozoic in the western margin of the sao francisco paleocontinent new in situ u pb and lu hf isotope analyses on detrital zircons by la mc icp ms were obtained for clastic sedimentary rocks of the paranoa group considered to be the oldest unit of the this sedimentary sequence the u pb data define a maximum depositional age of 1 54 ga and a minimum depositional age of 1 04 ga the latter obtained on diagenetic xenotime overgrowth on zircon grains combined u pb and lu hf data permitted to reconstruct the tectonomagmatic evolution of the potential source areas identified in the sao francisco craton two zircon populations at 1 54 and 1 78 ga with hf t values from 5 1 to 5 5 are possibly related with the mesoproterozoic extensional magmatism registered in the arai and espinhaco rifts located in the brasilia belt and in the sao francisco craton respectively the most important paleoproterozoic zircon population at 2 0 2 25 ga shows positive hf t 0 to 8 and paleoproterozoic tdm values indicating a continuous long period of magmatism with generation of juvenile crust during the paleoproterozoic two minor zircon populations at 2 1 and 2 15 ga showing negative hf t values 0 to 10 1 and tdm values between 2 65 and 3 22 ga may represent arc related magmatism with reworking of archean crust during the evolution of an active margin of the sao francisco craton a third minor zircons population at 2 05 ga with strongly negative hf t values between 8 6 and 17 7 and tdm values between 2 93 and 3 46 ga may represent a collisional magmatism that characterized the final stage of an active margin evolution with reworking of early archean crust several minor zircon populations of archean ages 2 7 2 85 3 1 and 3 42 ga derived from the archean nuclei in the interior of the sao francisco craton suggest the presence of different magmatic pulses that repeatedly reworked a juvenile paleoarchean crust the oldest event of generation of juvenile crust is registered by zircons with u pb age of 3 42 ga positive hf t values of 3 0 and tdm of 3 54 ga

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

origin of life from apatite dating mojzsis et al 1 2 reported the carbon isotope composition of carbonaceous inclusions in grains of apatite from sediment sequences of akilia island southwest greenland that are more than 3 850 million years myr old the 13c values measured by mojzsis et al 1 led them to conclude that these carbonaceous materials are evidence of early life 3 850 myr ago but if other isotopes u pb and pb pb are used the apatites are estimated at just 1 504 336 2 and 1 459 160 2 myr old this value is consistent with measurements of 1 600 1 700 myr for rb sr mineral isochrons on biotites3 and 1 670 myr for k ar muscovite4 from amitsog gneiss in the region we conclude that about 1 500 myr ago these apatites in akilia island experienced a metamorphic event of about 600 c estimated by the closure temperature of the u pb system5 6

shock metamorphism and petrography of the shergotty achondrite the shergotty subsamples 1 and 12 consist of augite and pigeonite 67 5 maskelynite 24 ilmenite and titanomagnetite 2 pyrrhotite 0 4 whitlockite 1 8 apatite 0 1 quartz 0 5 baddeleyite trace fayalite 0 4 mesostasis 3 and shock induced local polymineralic melt products 0 6 the overall modal composition is similar to other shergotty samples except for the rather high whitlockite content the shock effects observed in the mineral constituents include mosaicism deformation bands planar fractures and mechanical twin lamellae in clinopyroxene isotropization of plagioclase with very rare remnants of birefringence planar deformation structures mosaicism and strongly reduced birefringence in quartz mechanical twinning of ilmenite localized in situ melting of neighbouring minerals at the contact of low and high density phases based on the refractive index of maskelynite average 1 5467 with average an content of 49 and the degree of isotropization of the plagioclase an equilibrium shock pressure of 29 1 gpa is derived the inferred post shock temperature is 200 20 c no heating event could have exceeded 400 c duke 1968 local stress and temperature concentrations reach 60 80 gpa and 1600 2000 c the observed shock effects can be explained by a single shock event a second weaker shock event as found by others appears to be highly improbable equilibrium shock pressures and post shock temperatures for the other known shergottites are 31 2 gpa and 220 50 c zagami 43 2 gpa and 400 800 c alha 77005 the pressure estimate for eeta 79001 by lambert 1985 is confirmed 34 1 gpa the post shock temperature is 250 50 c the abundance and textural setting of localized melt products in these meteorites confirm increasing shock pressures in the sequence shergotty zagami eeta 79001 alha 77005 undoubtedly the melts could have been formed by the same single shock which produced the equilibrium shock effects e g maskelynitization in these meteorites the shock induced particle velocities inferred from hugoniot data of basalts are in the 1 5 2 0 km s range for the parental rocks of the shergottites ejection velocities are therefore in the order of 3 4 km s special ejection mechanisms are required in order to exceed the escape velocity of a planet like mars without producing higher degrees of shock e g melting than those observed in the shergottites

ion microprobe pb pb dating of carbonado polycrystalline diamond abstract we report in situ ion microprobe pb pb dating of quartz rutile and clay mineral inclusions and matrix part of polycrystalline diamonds carbonado derived from a proterozoic conglomerate in diamond bearing deposit of minas gerais in brazil together with u pb ages of zircons also extracted from the deposit thirty four spots on seven quartz grains located in the cavity of the gm01 carbonado yield 207pb 206pb isochron age of 3247 800 ma 2 mswd 0 75 and six spots on three rutile inclusions give the age of 3916 1300 ma 2 mswd 0 092 seven spots on three clay mineral inclusions of the do3 carbonado show common lead compositions while four spots on matrix define 207pb 206pb isochron age of 3811 1800 ma 2 mswd 0 012 seventy six spots on seventy zircon grains derived from the same conglomerate show three major u pb concordant ages of 2151 17 ma 2692 20 ma and 2931 22 ma with two concordant zircon outliers of 1726 58 ma and 3599 12 ma the youngest age is consistent with the formation age of 1750 1700 ma in the proterozoic conglomerate estimated by other workers the 3 6 ga zircon is the oldest record in the south american platform it may be detrital in origin and reflect the remnant of an archean craton the pb pb age of quartz and rutile inclusions in gm01 carbonado and that of do3 carbonado matrix are 3315 720 ma and 3811 1800 ma the matrix age is consistent with pb pb age of 2 6 3 8 ga of central african carbonados in the literature suggesting a close genetic relationship between brazilian and african carbonados

a discussion of isotopic systematics and mineral zoning in the shergottites evidence for a 180 m y igneous crystallization age abstract proposed igneous and metamorphic ages of the shergottites a suite of achondritic basaltic meteorites are examined in terms of the shergottites petrography and mineral chemistry no metamorphic or hydrothermal event appears capable of resetting the refractory sr and nd isotopic systems of the shergottites since the time of their igneous crystallization the approximately concordant rb sr 180 20 m y and u th pb 190 30 m y internal isochrons are thus interpreted as representing the time of igneous crystallization the sm nd internal isochrons which yield older apparent ages also show large scatter and are regarded as artifacts of the shergottites complex igneous history rubidium sr sm nd and pb pb wholerock isochrons are interpreted as mixing lines and are reasonably attributed to igneous processes such as wall rock assimilation and magma mixing if the shergottites are indeed less than 200 m y old they represent the youngest known extraterrestrial basalts this conclusion is supportive of the hypothesis that the snc meteorites are samples of the planet mars

uranium lead systematics of phosphates in lunar basaltic regolith breccia meteorite hills 01210 chronological studies of brecciated lunar meteorites have proved difficult because they are mixtures of materials from various sources and the radiometric clocks are sometimes affected by the subsequent impact events on the moon here we report the in situ u pb dating of phosphates in lunar meteorite meteorite hills met 01210 which is a regolith breccia consisting of low ti mare basalt clasts and mineral fragments with a minor anorthositic component in situ analyses of four merrillite and four apatite grains in met 01210 which are resistant to secondary events resulted in a 207pb 206pb 204pb 206pb isochron age of 3904 85 ma 95 confidence limit this phosphate formation age when considered as the crystallisation age of this low ti basalt is similar to crystallization ages of 3 8 3 9 ga for unbrecciated low ti basalt meteorites asuka 881757 and yamato 793169 this result reinforces the hypothesis that all these three meteorites originated from the same area on the moon and were launched by a single impact event consistent with the similarity of launch ages mineralogical and geochemical signatures

chemical systematics of the shergotty meteorite and the composition of its parent body mars abstract we report chemical data for 60 elements by inaa and rnaa in two bulk samples for 30 elements in various mineral separates of shergotty and results of leaching experiments with 1m hcl on powdered aliquots of shergotty and beta 79001 lithologies a and b shergotty is homogeneous in major element composition but heterogeneous with respect to lil trace elements 20 the heterogeneity is even greater for volatile and siderophile trace elements the mineral data including three clinopyroxene fractions with variable feo contents maskelynite and minor phases ti magnetite ilmenite quartz k rich phase show that major minerals do not account for the rare earth elements ree in the bulk meteorite instead the ree are to a large extent concentrated in accessory whitlockite and apatite shown by leaching with 1m hcl together with the majority of ree la 96 yb 70 cl and br are quantitatively dissolved by leaching the ree patterns of the leachate of shergotty and eeta 79001 are different the shergotty leachate may consist of two components component l is similar to that of eeta 79001 leachate whitlockite component 2 is enriched in light ree and may be responsible for the higher lree contents of shergotty in comparison to the other shergottites there is some evidence that shergotty was an open system and component 2 was introduced after crystallization the ree patterns of the residues of shergotty and eeta 79001 are identical indicating that the parent magmas of both meteorites are compositionally similar based on cpx separates with the lowest ree content the ree pattern in the shergotty parent magma was calculated it is enriched in lree and has a subchondritic nd sm ratio the negative eu anomaly in the phosphates indicates that at least some plagioclase crystallized before phosphate based on several element correlations in snc meteorites it was suggested dreibus and wanke 1984 that both the shergotty parent body spb very probably mars and the earth accreted from the same two chemically different components component a highly reduced and devoid of volatile elements and an oxidized component b containing also volatile elements the spb mars mantle is 2 4 times richer in volatile and moderately siderophile elements than the earth indicating a higher portion of component b in the spb the concentrations of chalcophile elements in the spb mantle are low reflecting equilibration with a sulfide phase and subsequent segregation of sulfide into the core unlike the earth wanke 1981 the spb mars may therefore have accreted almost homogeneously

sr and nd isotopic systematics of shergotty meteorite abstract strontium and neodymium isotopic measurements are reported on mineral separates whole rock samples and their leachates and residues of shergotty meteorite a very large variation of the sm nd ratio in the phosphates of shergotty is observed two sources of nd are observed which are not mixed completely within shergotty resulting in two ages 1 an apparent age of 147 20 m y from the whole rock leachateresidue nd trend and 2 360 16 m y from a well defined nd isochron of minerals and their leachates and residues about 60 of the sr in the rock resides in the plagioclase and mesostasis and this was reset at 167 m y for the pyroxenes this resetting event had a more complex but also a more localized effect from the general pattern of this resetting a shock event at this time seems possible the 360 m y whole rock leachate residue age in the rb sr isotopic system coincides with the sm nd isochron age we think that the 360 m y age represents the crystallization of shergotty the apparently younger nd age of the phosphates which are indicated by the leaching experiments might be caused by late or post magmatic contamination of the whitlockites with radiogenic nd this same contamination process must also have affected the sr isotopic system the 360 m y crystallization age implies that the plagioclase and phosphates behaved as an open system to the contaminant after the crystallization of the pyroxenes the sr of the contaminant affected both the plagioclase and whitlockite but nd influenced only the whitlockites reflecting the partitioning of sr and nd between these phases the general chemical pattern of this contamination process is different from contamination patterns observed in terrestrial rocks this pattern may represent the finger print of localized fluid rock interaction on mars since a similar trend is observed in other snc meteorites it could indicate that a potassium phase could be a mantle mineral on mars this would have important effects on the chemical evolution of a planet especially in respect to isotopic tracers like ar pb sr

uranium lead systematics of low ti basaltic meteorite dhofar 287a affinity to apollo 15 green glasses article i nfo dhofar 287 is a lunar meteorite found in oman in 2001 which consists of a major portion 95 of low ti mare basalt dho 287a and a minor attached part 5 of regolith breccia dho 287b here we report the u pb systematics of dho 287a using data collected with a sensitive high resolution ion microprobe shrimp in situ analyses of five merrillite and three apatite grains which are resistant to secondary petrologic events resulted in a total pb u isochron age of 3 34 0 20 ga in 238 u 206 pb 207 pb 206 pb 204 pb 206 pb 3 d space 95 confidence level the observed pb pb isochron of these eight phosphates coupled with four plagioclase grains alsoyieldeda 207 pb 206 pbageof3 35 0 13ga thisformationage whenconsideredasthecrystallizationageof

ion microprobe uranium thorium lead dating of shergotty phosphates we report ion microprobe u th pb dating of shergotty phosphates by means of the sensitive high resolution ion microprobe shrimp recently installed at hiroshima university japan ten analyses of whitlockite merrillite and three analyses of apatite indicate a 238u 206pb isochron age of 225 200 ma and a tera wasserburg concordia constrained linear three dimensional isochron age of 217 110 ma in the 238u 206pb 207pb 206pb204pb 206pb diagram these ages agree well with the 232th 208pb age of 189 83 ma which suggests that primary crystallization or a shock metamorphic event defined the formation age of the phosphate minerals the average of the later two ages 204 68 ma is consistent with the previously published rb sr age of 165 11 ma and u th pb age of 200 ma these show marginal agreement with the 40ar 39ar age of 254 10 ma but are significantly different from the sm nd age of 360 16 ma taking into account the closure temperature of the u pb system in apatite we suggest the time that shergotty last experienced a temperature of 900 c was 204 68 ma

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

thermoluminescence and the shock and reheating history of meteorites iii the shergottites abstract the thermoluminescence tl sensitivities of the four shergottites are extremely low and display a 10 fold range values are 0 15 to 1 8 where dhajala 1000 with the tl sensitivity decreasing with increasing peak temperature from about 140 to 180 c and peak width from about 100 to 150 c a mineral separation experiment indicates that the mineral producing the tl is associated with the maskelynite presumably nanogram per gram quantities of crystalline feldspar are present in the maskelynite samples of shergotty allan hills a77005 and elephant moraine a79001 were annealed at 400 900 c for 24 98 h for shergotty the peak increased in width and moved to higher temperatures in the glow curve while for allan hills a77005 and elephant moraine a79001 whose tl peaks were already broad and at high temperatures remained unchanged all samples showed a significant increase in tl sensitivity when annealed at 600 700 c apparently the feldspar is present in varying proportions of high to low temperature form and in amounts which vary from meteorite to meteorite we conclude that the shergottites underwent post shock recrystallization at a variety of cooling rates and that the order of increasing cooling rate was shergotty allan hills a77005 zagami and elephant moraine a79001 the presence of a high temperature phase implies peak post shock cooling temperatures 600 c and that the size of the ejecta was

ion microprobe u pb dating and ree analyses of phosphates in h4 chondrite yamato 74371 1 u and pb isotopes and rare earth elements rees in individual phosphate grains from h4 chondrites y 74371 were measured by using an ion microprobe nine analyses of whitlockite merrillite and five analyses of apatites indicate a total pb u isochron age of 4533 40 ma 2 sigma which are consistent with the results from previous using thermal ionization mass spectrometer tims the observed apatites age of 4525 30 ma 2 sigma however is younger than those of previous works on the other hand the time difference between the whitlockite age of 4601 94 ma 2 sigma and those of apatites are not observed because of the large uncertainties the ree abundance patterns of the whitlockites normalized to ci chondrite are characterized by an almost constant enrichment of 200 800 times ci abundance and a striking negative eu anomaly the ree abundances of the apatites are lower than those of whitlockite grains and vary appreciably among different grains the remarkable correlation between the eu anomaly eu eu and total concentration of ree is confirmed but significant correlation with eu anomaly and formation age of individual grains are not observed

rare earth element carriers in the shergotty meteorite and implications for its chronology ion probe measurements of the rare earth element ree concentrations of individual grains of the shergotty meteorite are reported phases analyzed include whitlockite apatite baddeleyite augite pigeonite maskelynite and k rich glass u concentrations of whitlockite and apatite crystals were also obtained the whole rock ree pattern is dominated by whitlockite which contains over 95 of the light rare earth elements lree ree concentrations in apatite are much lower than estimated by laulet al 1986 all the whitlockites whether intergrown with pyroxene equant or interstitial have the same relative abundances of lree i e patterns are almost flat from la to sm the observation by joneset al 1985 of a skeletal whitlockite with lree enrichment is not confirmed by analyses of the same grain pyroxene rims are not enriched in lree no leachable carrier enriched in lree and associated with pyroxene laulet al 1986 jagoutz and wanke 1986 has been found instead either a laboratory contamination or a petrographically cryptic phase such as a film on grain boundaries is suspected as the carrier of lree enrichments if a grain boundary film carries the enrichments it would not be resistant to the metamorphic resetting which has affected other isotopic reservoirs in this sample thus there is no compelling reason to consider the sm nd pyroxene leachates line jagoutz and wanke 1986 as a 360 m y isochron estimates of ree abundances in the shergotty intercumulus melt indicate that a complex petrogenesis is required in agreement with the conclusions of mckayet al 1986a pyroxene distribution coefficients measured experimentally mckayet al 1986a are compared with estimates from measured ree abundances in augite and pigeonite evolution of ree abundances in the shergotty late stage interstitial melt as inferred from analyses of whitlockite conforms with trends predicted from partitioning considerations and requires no special processes such as metasomatism the average u concentrations of whitlockite and apatite are respectively 540 and 1 550 ppb although the calcium phosphates are enriched in u they contain less than 20 of the u in shergotty

formation ages and evolution of shergotty and its parent planet from u th pb systematics the isotopic composition of lead was determined in different phases from shergotty zagami and eeta 79001 using phases with low 238 u 204 pb the initial leads of these meteorites could be well defined and are distinct from each other and have high 204 pb 206 pb from 0 0652 to 0 0739 these leads evolved in different reservoirs over most of solar system history in a low 238 u 204 pb 5 environment it follows that the parent planet of the shergottites has a high 204 pb concentration relative to u and must also be high in other volatiles if the parent planet of the shergottites is mars then this planet must be volatile rich compared to the earth by a factor of 1 8 this implies that mars lost its original atmosphere and that the present atmosphere was derived from a previously outgassed martian upper mantle the u th pb isotopic relationships involving phases with high 238 u 204 pb are quite regular and give ages for three shergottites which indicate an event of u th pb fractionation at 200 m y the initial leads at that time were highly evolved relative to the primordial lead the absence of substantial additions of radiogenic lead above the initial lead in high u phases precludes an older age for the u th pb fractionation however details of the data arrays are complex the young age is in general agreement with some of the ages obtained by other methods but precise concordance between the different methods is not established it is suggested that the shock event that produced maskelynite may possibly be associated with the late stage breakup at 2 5 m y and not necessarily related to the 180 m y record the major event of chronometer resetting is taken to be 180 m y this event does not appear to be an endogenic igneous event but an almost complete equilibration during a major impact on more ancient igneous rocks which were contained in the target problems of the polymetamorphic history of meteorites appear as complicated as those of polymetamorphic terrestrial terranes

palaeoproterozoic thermal events recorded in the 4 0 ga acasta gneiss canada evidence from shrimp u pb dating of apatite and zircon u pb isotopes of apatites and zircons extracted from a sample of the acasta gneisses that occurs along the western margin of the slave craton in northwest territories of canada have been measured using a shrimp ii ion microprobe eleven apatite analyses 30 m spot give 238u 204pb 206pb 204pb and 204pb 206pb 207pb 206pb isochron ages of 1905 86 ma 2 and 1936 28 ma 2 respectively analyses 20 m spot on the partly recrystallised central portions of fourteen zircons mostly define a mixing array on a 238u 206pb 207pb 206pb concordia plot with concordia intercepts at 4014 25 ma 2 and 1967 93 ma 2 the former agrees with 3 96 4 02 ga protolith ages obtained on the oldest components of the acasta gneisses by other workers the lower concordia intercept for the zircon data is consistent with the u pb age of apatites and may be related to a 500 c thermal event perhaps early in the palaeoproterozoic wopmay orogeny