chemical studies of h chondrites i mobile trace elements and gas retention ages abstract trends for 16 trace elements ag as au bi cd co cs ga in k rb sb se te tl and zn chosen to span a broad geochemical and thermal response range in 44 h4 6 chondrites differ widely from those in l4 6 chondrites in particular h chondrites classified as heavily shocked petrologically do not necessarily exhibit 40 ar loss and vice versa the clear cut causal relationship between siderophile and mobile element loss with increasing late shock seen in l chondrites is not generally evident in the h group h chondrite parent material experienced an early high temperature genetic episode that mobilized a substantial proportion of these trace elements so that later thermal episodes resulted in more subtle collateral fraction ations mildly shocked l chondrites escaped this early high temperature event indicating that the two most numerous meteorite groups differ fundamentally in genetic history

chemical characteristics and origin of h chondrite regolith breccias abstract we report petrologic data and contents of ag bi cd co cs ga in rb se te tl and zn trace elements spanning the volatility mobility range in light and dark portions of h chondrite regolith breccias and l chondrite fragmental breccias the chemical petrologic characteristics of h chondrite regolith breccias differ from those of non brecciated chondrites or fragmentai breccias petrologic characteristics and at least some trace element contents of h chondrite regolith breccias reflect primary processes contents of the most volatile mobile elements may reflect either primary or secondary processing possibly within layered h chondrite parent object s chemical petrologic differences existed in different regions of the parents regolith formation and gardening and meteoroid compaction were not so severe as to alter compositions markedly

how many paleointensity determinations are required from a single lava flow to constitute a reliable average 1 statistical analysis has been undertaken to investigate the minimum number of paleointensity estimates required to allow certainty at the 95 confidence limit that the mean is within 10 of the implied true mean for an entire lava flow the data used for the analysis was provided by previous paleointensity studies which used three different methods thellier coe shaw and microwave thellier on 19 or more samples from three different basalt lava flows the results strongly suggest that future paleointensity studies need to produce many more estimates per lava flow than is currently the norm in order to ensure that the calculated mean paleointensity does not differ significantly from the true flow mean furthermore they indicate that a low measured dispersion for a small number of estimates is not a safeguard against misrepresentation of the flow mean paleointensity finally we provide quantitative evidence that paleointensity studies should always attempt to maximise vertical coverage of lava flows to avoid biasing of the mean

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

ages of 24 widespread tephras erupted since 30 000 years ago in new zealand with re evaluation of the timing and palaeoclimatic implications of the lateglacial cool episode recorded at kaipo bog abstract tephras are important for the nz intimate project because they link all three records comprising the composite inter regional stratotype developed for the new zealand climate event stratigraphy nz ces here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30 000 calendar cal years ago in new zealand to help facilitate their use as chronostratigraphic dating tools for the nz ces and for other palaeoenvironmental and geological applications the selected tephras comprise 12 rhyolitic tephras from taupo nine rhyolitic tephras from okataina one peralkaline rhyolitic tephra from tuhua and one andesitic tephra each from tongariro and egmont taranaki volcanic centres age models for the tephras were obtained using three methods i 14 c based wiggle match dating of wood from trees killed by volcanic eruptions these dates published previously ii flexible depositional modelling of a high resolution 14 c dated age depth sequence at kaipo bog using two bayesian based modelling programs bacon and oxcal s p sequence function and the intcal09 data set with sh offset correction 44 17 yr and iii calibration of 14 c ages using oxcal s tau boundary function and the shcal04 and intcal09 data sets our preferred dates or calibrated ages for the 24 tephras are as follows youngest to oldest all mid point or mean ages of 95 probability ranges kaharoa ad 1314 12 taupo unit y ad 232 10 mapara unit x 2059 118 cal yr bp whakaipo unit v 2800 60 cal yr bp waimihia unit s 3401 108 cal yr bp stent unit q 4322 112 cal yr bp unit k 5111 210 cal yr bp whakatane 5526 145 cal yr bp tuhua 6577 547 cal yr bp mamaku 7940 257 cal yr bp rotoma 9423 120 cal yr bp opepe unit e 9991 160 cal yr bp poronui unit c 11 170 115 cal yr bp karapiti unit b 11 460 172 cal yr bp okupata 11 767 192 cal yr bp konini bed b 11 880 183 cal yr bp waiohau 14 009 155 cal yr bp rotorua 15 635 412 cal yr bp rerewhakaaitu 17 496 462 cal yr bp okareka 21 858 290 cal yr bp te rere 25 171 964 cal yr bp kawakawa oruanui 25 358 162 cal yr bp poihipi 28 446 670 cal yr bp and okaia 28 621 1428 cal yr bp secondly we have re dated the start and end of the lateglacial cool episode climate event nzce 3 in the nz ces previously referred to as the lateglacial climate reversal as defined at kaipo bog in eastern north island new zealand using both bacon and oxcal p sequence modelling with the intcal09 data set the ca 1200 yr long cool episode indicated by a lithostratigraphic change in the kaipo peat sequence to grey mud with lowered carbon content and a high resolution pollen derived cooling signal began 13 739 125 cal yr bp and ended 12 550 140 cal yr bp mid point ages of the 95 highest posterior density regions bacon modelling the oxcal modelling generating almost identical ages confirmed these ages the lateglacial cool episode ca 13 8 12 6 cal ka bp thus overlaps a large part of the entire antarctic cold reversal chronozone ca 14 1 12 4 cal ka bp or ca 14 6 12 8 cal ka bp and an early part of the greenland stadial 1 younger dryas chronozone ca 12 9 11 7 cal ka bp the timing of the lateglacial cool episode at kaipo is broadly consistent with the latitudinal patterns in the antarctic cold reversal signal suggested for the new zealand archipelago from marine and terrestrial records and with records from southern south america

chemical studies of h chondrites 5 temporal variations of sources we report 36cl 301 kyr half life data obtained by accelerator mass spectrometry allowing nominal terrestrial ages to be determined for 39 antarctic h4 6 chondrites for which contents of volatile trace elements are known the compositional difference between these antarctic meteorites and 58 non antarctic falls increases with terrestrial age and using multivariate statistical techniques becomes highly significant for antarctic samples with ages 50 kyr the compositional difference is inconsistent with trivial causes such as weathering and seems to reflect differences in thermal histories of parent sources temporal source variations for the h chondrite flux on earth thus exist not only on a short term 40 years basis dodd et al 1993 but also on a long term 50 kyr basis

chemical studies of differentiated meteorites i labile trace elements in antarctic and non antarctic eucrites abstract we report data for ag au bi cd co cs ga in rb sb se te tl u and zn determined by rnaa in 25 antarctic and 9 non antarctic eucrites including the cumulate eucrites moore co and serra de mage compositional variations for a given element in a population range from

penecontemporaneous metamorphism fragmentation and reassembly of ordinary chondrite parent bodies the occurrence and proportions of petrologic types among ordinary chondrites have been explained by internal heating of three h l ll parent asteroids of 100 km radius e g miyamoto et al 1982 this conventional onion shell model predicts an inverse relation between petrologic type and metallographic cooling rate but none has been observed scott and rajan 1981 devised a metamorphosed planetesimal model to explain this discrepancy whereby metamorphism occurs in planetesimals a few kilometers in radius which then accrete to form r 100 km parent bodies metallographic cooling rates are then controlled by burial depth thermal and collisional constraints on the metamorphosed planetesimal model are examined here and the model is found to be applicable only to highly insulating 26al rich planetesimals that can accrete intact without being shattered by impact or to shattered planetesimals whose fragments are not widely dispersed over the target surface an alternative model is presented here in which onion shell parent bodies are collisionally fragmented during metamorphism and then gravitationally reassembled if reassembly times are short days then metallographic cooling rates would be determined by burial depth in the reaccreted parent body this model unlike previous ones can explain both coherent and incoherent cooling rates of breccia clasts by collisions during or after metamorphism respectively

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

growth of a young frequently active composite cone ngauruhoe volcano new zealand ngauruhoe cone in southern taupo volcanic zone new zealand has grown rapidly over the last 2 500 years in an alternation of effusive strombolian vulcanian and sub plinian eruptions of andesitic magma at times growth has been staccato in fashion as evidenced in the historical record each historical eruption typically lasted days to months alternating with repose periods of years to decades major historic eruptions occurred in 1870 1949 1954 1955 and 1973 1975 encompassing wide variations in eruptive style over short timescales the early period of cone building appears to have been dominated by a more continuous form of activity characterised by a series of numerous frequent explosive eruptions with associated lava flows the 2 2 km3 cone has grown in a piecemeal sectorial manner reflecting constant modification to the morphology of the summit which has funnelled eruption products to specific sectors of the cone eruption rates can be calculated on several different timescales discharge rates averaged over individual eruptive pulses vary by two orders of magnitude 2 7 280 m3 s 1 reflecting variations in high level magma ascent rates and processes such as degassing which are in turn reflected in contrasting eruptive styles lower rates e g 0 65 m3 s 1 are obtained by averaging the discharge over an entire eruption lasting several months and may correspond to the ascent rate of magma batch es feeding the eruption the long term growth rate of ngauruhoe is 0 9 km3 ky 1 this is an average rate reflecting the long term deep supply rate of magma to crustal reservoirs by looking at eruption rates on these different timescales we are better able to constrain processes occurring at various depths within the plumbing system there are few detailed studies of the growth patterns of young volcanic cones but such data are essential in understanding the dynamics of andesitic systems more than 60 lavas and pyroclastic units mapped on different sectors of ngauruhoe cone have been correlated by flow chronology and their distinctive compositions into five groups although the cone has grown rapidly ngauruhoe shows little evidence for the existence of large crustal magma reservoirs and long lived magma batches instead abrupt and non systematic changes in magma chemistry and isotopic composition between and within the five groups indicate that the volcano has an open system multi process multi directional character and erupts small 0 1 km3 and short lived 100 103 years magma batches with no simple time composition relationships between successive batches

linking distal volcaniclastic sedimentation and stratigraphy with the development of ruapehu volcano new zealand long lived stratovolcanoes are often characterized by cycles that include pulses of explosive and effusive eruptive activity periodic flank collapses and long periods of eruptive quiescence reconstructing these solely from exposures on volcanic edifices is difficult because deposits are dominantly from comparatively recent reconstruction episodes while older sequences are buried or have long been eroded long runout mass flow deposits on the other hand offer insights into the older eruptive history and long term eruptive behavior of composite volcanoes at mt ruapehu new zealand 40ar 39ar dating of lava clasts within distal mass flow sequences combined with new mapping and sedimentological descriptions reveal three hitherto unknown eruptive episodes of the volcano and extend its minimum age to at least 340 ka plinian to subplinian eruptions were followed by periods of subdued volcanic activity voluminous 1 km3 inter eruptive flank failures were precursors to major reconstruction episodes associated with numerous syn eruptive mass flows emplaced up to 90 km from the volcano syn eruptive collapse triggered large plinian eruptions associated with pyroclastic density currents rapid ring plain aggradation dominated during periods of subdued volcanic activity when intensive edifice erosion induced frequent inter eruptive lahars

compositions of three low feo ordinary chondrites indications of a common origin with the h chondrites abstract burnwell eet 96031 and lap 04575 are ordinary chondrites oc that possess lower than typical olivine fa content than has been established for the h chondrites

paleointensities for 10 22 ka from volcanic rocks in japan and new zealand abstract eight volcanic rocks from japan and new zealand in the age range 10 50 ka b p were studied using the thellier method paleointensity experiment and yielded five successful results for 10 22 ka samples from the shikotsu kuttara and daisen volcanoes in japan were taken from pyroclastic flows both welded and non welded and a pumice fall deposit one of the two new zealand rocks is a rhyolite lava from the taupo volcanic zone four sites out of seven located on rocks that are not usually subjected to thellier s experiment yielded successful results which indicates that volcanic products such as pyroclastic flows and rhyolite lavas are as good a material as basalt and andesite lavas for application of the paleointensity experiment one paleointensity from new zealand at 9 9 ka is very large at about 100 t and provides support for the paleointensity high found in europe and japan 1 2 the other four paleointensities for 14 22 ka are smaller than the present day value and this agrees with the idea of a broad paleointensity minimum for the period 10 50 ka that was suggested by mcelhinny and senanayake 3 it is also noted that the variation curve of absolute paleointensity from the volcanic rocks is reasonably similar to the relative paleointensity curves from marine and lake sediments which were summarized by tauxe 4

40ar 39ar geochronology of magmatic activity magma flux and hazards at ruapehu volcano taupo volcanic zone new zealand we have determined precise eruption ages for andesites from ruapehu volcano in the tongariro volcanic centre of the taupo volcanic zone tvz using 40ar 39ar furnace step heating of separated groundmass concentrates the plateau ages indicate several eruptive pulses near 200 134 45 22 and 300 m section of lavas in whangaehu gorge as well as some lavas in ohinepango and waihianoa catchments on eastern ruapehu and this suite of lavas belongs to the waihianoa formation this pulse of activity is not represented on nearby tongariro volcano indicating that the two volcanoes have independent magmatic systems a younger group of lavas yields dates between 50 and 20 ka and includes lava flows from the turoa skifield and in the ohinepango and mangatoetoenui catchments and is consistent with two pulses of magmatism around the time of the last glacial maximum relating it broadly to the mangawhero formation syn and post last glacial activity lavas with ages 15 ka are assigned to the whakapapa formation and include the voluminous flows of the rangataua member on southern ruapehu magma flux integrated over 1000 yr periods averages 0 6 km3 ka 1 assuming a volcano lifespan of 250 ka fluxes for the te herenga waihianoa and mangawhero formations are consistent at 0 93 0 9 and 0 88 km3 ka 1 respectively these fluxes are broadly comparable with those measured at other modern andesite arc volcanoes e g ngauruhoe 0 88 merapi 1 2 and karymsky 1 2 km3 ka 1 the relatively low flux 0 17 km3 ka 1 calculated for the whakapapa formation may derive from underestimates of erupted volume arising from an increase in phreatomagmatic explosive eruptions in postglacial times however using volume estimates for the 1995 1996 eruptions and a recurrence interval of 25 yr has yielded an integrated 1000 yr flux of 0 8 km3 ka 1 in remarkable agreement to estimates for the prehistoric eruptions overall ruapehu shows consistency in magma flux but at time scales of the order of one hundred to some thousands of years field evidence suggests that short bursts of activity may produce fluxes up to twenty times greater this is significant from the perspective of future activity and hazard prediction

chemical studies of l chondrites iii mobile trace elements and ar 40 ar 39 ages abstract we report data for trace elements ag au bi cd co cs ga in rb se te tl and zn determined by radiochemical neutron activation analysis in l4 6 chondrites with undisturbed 40 ar release patterns or with patterns showing some disturbance in the 4 4 4 6 gyr plateau indicating shock induced loss mean concentrations are lower many significantly so in 16 chondrites with disturbed patterns than in 4 with undisturbed ones consistent with shock induced mobilization similar trends were noted earlier in l4 6 chondrites having mineralogically observable shock indicators mean concentrations are lower in strongly shocked i e 22 gpa than in mildly shocked 40 ar release patterns are mildly shocked but chondrites with disturbed patterns are more strongly heated on average than those of shock facies d f i e 22 to 57 gpa pooling these populations significantly lower mean concentrations of nearly all trace elements in 26 strongly shocked l4 6 chondrites than in 14 mildly shocked ones indicate loss in shock formed fes fe eutectic and or by vaporization during cooling of shock heated collisional debris two element correlations and the pattern of them i e correlation profiles are also consistent with this picture trace elements can act as thermometers for collisional episodes in l4 6 chondrites but not for earlier thermal fractionations unless compensation can be made for late shock heating

high carbon concentrations in meteoritic chondrules a record of metal silicate differentiation abstract both reduced type i and oxidized type ii chondrules from the primitive chondrites allende semarkona and bishunpur were analysed with ion microprobe for the carbon and hydrogen concentrations of their silicates the high and variable h and c concentrations found i e from 100 to 1500 ppm h 2 o and from 100 to 3900 ppm c show that these volatile elements were present in chondrule precursors as solid grains mean c concentrations are 3 times higher in type i chondrules than in type ii chondrules therefore it seems likely that metal silicate oxydo reduction reactions were promoted by c rich grains whose heterogeneous distribution in the protosolar nebula caused the variation in the redox states of chondrules based on the present results an in situ reduction of the silicates during chondrule melting seems plausible although reduction in the gas phase before condensation cannot be ruled out calculations of the devolatilisation rate of co from hot chondrules account for the presently measured high c concentrations of type i chondrules if 2 6 wt c grains were originally present among chondrule precursors such a result is in agreement with the c concentration in c1 chondrites and with laboratory simulations which have demonstrated that up to 4 wt c grains were necessary to yield type i chondrules by in situ reduction connolly et al 1994 assuming a solar c o ratio in the chondrule forming regions of the protosolar nebula it is likely that the high density of c grains in the gas resulted from presolar chemistry this interpretation is supported by the corresponding c grain atom gas ratio 2 7 10 13 which is 10 times below the ratio measured in the prestellar clouds

an h chondrite stream identification and confirmation fall data indicate that a significant elongate cluster of co orbital h chondrite falls in may between 1855 and 1895 h cluster 1 records encounters with two or three closely spaced and probably related meteoroid stream components each of which was met near its perihelion although meteorites included in the cluster vary widely in petrographic type 3 6 shock facies a d and 21ne exposure age 5 to 50 ma they have a distinct labile trace element signature that confirms a common thermal history and thus a common source region within an h chondrite parent body hence meteorites selected by one criterion fall parameters as distinguishable from all other h chondrites are distinguished from them by another completely different criterion contents of labile trace elements

curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods 1 the present study is aimed at improving the calibration of the compositional dependence of the curie temperature tc of titanomagnetite tmt on the basis of temperature dependent magnetic susceptibility c t curves measured on synthetic tmts in the fe ti o system in order to assess the possible influence of high temperature cation vacancies onto the tc values we have synthesized two types of assemblages in subsolidus conditions at 1 bar 1100c and 1300c under controlled oxygen fugacity conditions tmts synthesized in equilibrium with ilmenite hematitess ilmss are expected to have the highest vacancy concentrations those in equilibrium with wustite wus the lowest the composition and homogeneity of the synthetic tmts were carefully checked with a scanning electron microscope sem and an electron microprobe emp tc was determined from c t curves using a kappabridge and for comparison from ms t curves measured with a variable field translation balance our data set shows systematically higher tc values for tmt coexisting with ilmss than for tmt coexisting with wus most c t curves are nonreversible whereby the largest dtc 40 k concern tmt ilmss o f intermediate compositions synthesized at 1300c nonreversibility is interpreted as reflecting cation reordering in tmt during the high temperature c t measurements tc values obtained from ms t curves are higher than those obtained from the c t curves whereby the difference regularly increases up to 40 k with increasing ti content up to xusp 0 6 our new calibration curves are suitable to retrieve tmt compositions in basalts that were rapidly cooled and not oxidized by deuteric or hydrothermal fluids citation lattard d r engelmann a kontny and u sauerzapf 2006 curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods j geophys res 111 b12s28

formation conditions of igneous regions in ordinary chondrites chico rose city and other heavily shocked h and l chondrites we report microprobe and radiochemical neutron activation analysis rnaa data for hosts and igneous inclusions in the heavily shocked ordinary chondrites rose city h5 yanzhuang h6 farmington l5 malakal l5 chantonnay l6 chico l6 and tuan tuc l6 based on these analytical results equilibrium crystallization calculations ghiorso and sack 1995 phase equilibrium analysis e g sack and ghiorso 1994a b sack et al 1994 and experimental cooling rate studies e g walker et al 1976 we have assessed the metamorphic and magmatic histories of these seven heavily shocked chondrites we infer that 1 unfractionated chondritic liquids were intruded to depths 0 1 km in the parent asteroid of rose city 2 early chondritic liquids experiencing 5 10 olivine fractionation were erupted onto the surface of the parent asteroid s of yanzhuang and chantonnay and 3 near surface crystallization is also indicated for the liquids in tuan tue and farmington with chico and malakal crystallizing at slightly greater depths in all but chantonnay liquids appear to have derived from melting of chondrite types corresponding to their hosts in the l chondrite chantonnay the intrusive liquids derive from melting an h chondrite source region in which chondritic melts were stored for a sufficient time to produce pigeonite in zoned pyroxene xenocrysts heating effects are also reflected in the trace element contents of the chondrites our rnaa data for rose city seem to reflect only the siderophile lithophile fractionation evident in the metal distribution the yanzhuang rnaa data are generally similar to those of other h chondrites severe shock not involving phase transport seems to leave h chondrites unaffected compositionally contents of the four most mobile elements cd bi t1 in and cs in chico indicate loss so that this assemblage experienced extended low temperature cooling after injection of dike material into the chico host rnaa data for the other four l chondrites examined indicate more rapid cooling

h chondrites trace element clues to their origin we have analyzed 10 h chondrites for 20 trace elements using rnaa the meteorites included 4 of petrologic type 4 and 2 each of types 3 5 and 6 the data show that h chondrites are not isochemical h3 s are depleted by some 10 not only in fe dodd 1976 but also in the siderophiles os re ir ni pd au and ge moreover the abundance pattern of siderophiles varies systematically with petrologic type as similar fractionations of ree have been observed by nakamura 1974 it appears that both the proportions and compositions of the main nebular condensates varied slightly during accretion of the h chondrites thus the higher petrologic types are independent nebular products not metamorphosed descendants of lower petrologic types abundances of highly volatile elements cs br bi tl in cd ar36 correlate with petrologic type declining by 10 3 from type 3 to type 6 the trends differ from those for artificially heated type 3 s ikramuddinet al 1977b herzoget al 1979 but agree passably with theoretical curves for nebular condensation apparently the low volatile contents of higher petrologic types are a primary feature not the result of metamorphic loss the mineralogy of chondrites suggests that they accreted between 405 k absence of fe3o4 and 560 k presence of fes and the abundances of tl bi and in further restrict this interval to 420 500 k accretion at 1070 100 k as proposed by hutchisonet al 1979 1980 leads to some extraordinary problems volatiles must be injected into the parent body after cooling which requires permeation of the body by 1011 times its volume of nebular gas this process must also achieve a uniform distribution of the less volatile elements rb cu ag zn ga ge sn sb se f without freezeout in the colder outer layers factor analysis of our data shows 3 groupings siderophiles os re ir ni pd au and ge volatiles ag br in cd bi and tl and alkalis rb and cs the remaining 5 elements u zn te se and sb remain unassociated

chemical studies of l chondrites ii shock induced trace element mobilization abstract previous studies of chondrites heated in the laboratory for extended periods under conditions approximating those in shock heated collisional debris indicate that au co se ga rb cs te bi in ag zn tl and cd progress in mobility we report data for these 13 trace elements in 14 l4 6 chondrites of established shock history and discuss these and 13 additional chondrites studied earlier trace element contents vary with petrologic type s fe sub group and shock history the last dominating strongly absolute abundances and interelement relationships for the 6 or 7 most mobile elements vary with degree of shock loading i e residual temperatures established from mineralogic petrologic study a tertiary process shock heating previously known to have affected radiogenic 40 ar and or 4 he in meteorites but not other elements apparently was at least as effective as other open system processes secondary parent body and primary nebular and or accretionary episodes in establishing mobile trace element contents of l chondrites and probably others if conditions during early genetic episodes are to be deduced from compositional information shocked meteorites should be avoided or effects of later processes should be compensated for

igneous inclusions from ordinary chondrites high temperature cumulates and a shock melt we report microprobe instrumental neutron activation analysis and radiochemical neutron activation analysis data for three large igneous inclusions in the yamato y 75097 y 793241 and y 794046 ordinary chondrites the inclusions in the first two chondrites are troctolitic cumulates that have undergone appreciable reactions with their hosts either during emplacement and or cooling olivine spinel fe mg exchange pairs in these two inclusions record equilibration temperatures of about 710 c and these temperatures are similar to those exhibited by mineral pairs in the y 75097 and y 793241 hosts the inclusion in y 794046 is texturally unique consisting of fine grained randomly distributed olivines coarse 2 mm fascicular pyroxene laths and angular pockets of maskelynite plagioclase feldspar the phase compositions are readily interpreted as having resulted from extremely rapid essentially isochemical cooling to temperatures 1670 c we suggest that this igneous inclusion formed in situ by shock

paleointensity determination from sao miguel azores archipelago over the last 3 ka elsevier editorial system tm for physics of the earth and planetary interiors manuscript draft manuscript number pepi d 14 00015 title paleointensity determination from sao miguel azores archipelago over the last 3 ka article type research paper keywords paleomagnetism paleointensity azores atlantic ocean global spike corresponding author dr anita di chiara corresponding author s institution usp first author anita di chiara order of authors anita di chiara lisa tauxe prof fabio speranza dr abstract paleointensity data from the atlantic ocean are rare we present new paleointensity data from sao miguel azores islands portugal based on 20 paleomagnetic sites from 13 lava flows emplaced over the last 3 000 years ten lava flows are radiocarbon dated moore 1990 1991 moore and rubin 1991 whereas three flows were archeomagnetically dated by di chiara et al 2012 and one site was dated using stratigraphic relations all the samples previously investigated to recover paleodirections di chiara et al 2012 were subjected to izzi experiments importantly the new data are internally consistent agree with moroccan and european datasets and offer new constraints for cals style models e g korte and constable 2011 the inferred virtual axial dipole moments vadms range from 68 2 zam2 and 163 5 zam2 a peak in field strength with an estimated age of around 600 bce is well supported by two sites from the same flow furna and is comparable to the spike of intensity found in portugal of the same age nachasova et al 2009 and at about 1000 bce in the levant ben yosef et al 2009 shaar et al 2011 a gradient in vadm values with latitude observed by mitra et al 2013 between 100 to 1000 ad is confirmed as well as its absence from between 0 to 100 ad

absolute paleointensity and magnetomineralogical changes determinations of absolute paleointensity are often hampered by magnetomineralogical changes produced within samples of lava flows during successive heatings such changes which directly affect the capacity for a sample to acquire a partial thermoremanent magnetization ptrm are reflected by negative ptrm checks a deviation between the original ptrm and a repeated measurement after heating at a higher temperature because the deviations indicated by the ptrm checks can provide a direct estimate of the effects to the ptrms we suggest that they can be used to correct ptrms the correction method we present requires additional measurements in particular ptrm checks performed after each ptrm and specific diagrams to detect acquisition of chemical remanence performing multiple successive ptrm checks can also provide information on the blocking temperatures of the alteration product these experiments conducted on lava flows from different localities show that the magnetomineralogical changes mainly involved grains with blocking temperatures lower than the last heating step the corrections have been tested on recent and historic lava flows from several localities we have also compared results on samples from the same lava flows that were heated in air and in vacuum the mean paleointensity values were found to lie within less than 10 from the expected field intensity at each site the corrections resulted in the recovery of reliable paleointensity determinations for about twice as many specimens heated in vacuum and 65 additional data for specimens heated in air successive heatings at the same temperature in air are often accompanied by a time dependent oxidation of the natural remanent magnetization which is responsible for paleointensity values lower than the expected field a problem that is not related to the corrections we conclude that corrections can be used with fairly high confidence to the ptrms performed in vacuum and in air

chemical studies of h chondrites 8 on contemporary meteoroid streams using date and time of fall and petrographic classification as criteria many equilibrated h chondrites that fell during september and october from 1812 to the present form four significant clusters denoted as cluster 2 through cluster 5 on day year plots using radiochemical neutron activation analysis we determined 15 trace elements u au co sb ga rb ag se cs te zn cd bi tl and in ordered by increasing putative volatility during nebular condensation in 27 members of these four clusters we used model dependent and model independent multivariate statistical techniques to compare contents of the 10 most volatile elements separately in the four clusters with those of a 33 member suite of random h chondrite falls from 1773 to 1970 the clusters 2 and 5 suites that fell in september 1880 1991 and october 1919 1984 respectively each of which is represented by 10 h chondrite falls are not compositionally distinguishable from the suite of random falls however the 17 member combined suite of clusters 3 and 4 chondrites that fell during september october 1812 1992 proves compositionally distinguishable from random falls at moderate to strong significance levels of 0 01 0 001 this 17 member suite is less readily distinguished from random falls than are the previously reported suite of cluster 1 falls may 1855 1895 or antarctic h chondrites with nominal terrestrial ages 50 kyr each of which is highly significant at 0 001 levels all suites are genomict and exhibit a range of cosmic ray exposure ages with a plurality having 6 8 ma ages inconclusive results are obtained in the cases of clusters 2 and 5 however three h chondrite suites clusters 1 3 and 4 distinguishable from the random background by one property time of fall are also distinguishable by another contents of volatile trace elements or thermal history temporal change of h chondrite sources sampled by earth are indicated by these data

silver isotope variations in chondrites volatile depletion and the initial 107pd abundance of the solar system abstract the extinct radionuclide 107pd decays to 107ag half life of 6 5 ma and is an early solar system chronometer with outstanding potential to study volatile depletion in the early solar system here a comprehensive ag isotope study of carbonaceous and ordinary chondrites is presented carbonaceous chondrites show limited variations e107ag 2 1 to 0 8 in ag isotopic composition that correlate with the pd ag ratios assuming a strictly radiogenic origin of these variations a new initial 107pd 108pd of 5 9 2 2 10 5 for the solar system can be deduced comparing the pd ag and mn cr data for carbonaceous chondrites suggests that mn cr and pd ag fractionation took place close to the time of calcium aluminium rich inclusion cai and chondrule formation 4568 ma ago using the new value for the initial 107pd abundance the revised ages for the iron rich meteorites gibeon iva 8 5 3 2 4 6 ma grant iiiab 13 0 3 5 4 9 ma and canyon diablo ia 19 5 24 1 10 4 ma are consistent with cooling rates and the closure temperature of the pd ag system in contrast to carbonaceous chondrites ordinary chondrites show large stable isotope fractionation of order of 1 permil for 107ag 109ag this indicates that different mechanisms of volatile depletion were active in carbonaceous and ordinary chondrites nebular processes and accretion as experienced by carbonaceous chondrites did not led to significant ag isotope fractionation while the significant ag isotope variations in ordinary chondrites are most likely inflicted by open system parent body metamorphism

silver contents and cu ag ratios in martian meteorites and the implications for planetary differentiation abstract silver and cu show very similar partitioning behavior in sulfide melt silicate melt and metal silicate systems at low and high pressure temperature p t experimental conditions implying that mantle melting fractional crystallization and core mantle differentiation have at most modest within a factor of 3 effects on cu ag ratios for this reason it is likely that cu ag ratios in mantle derived magmatic products of planetary bodies reflect that of the mantle and in some circumstances also the bulk planet composition to test this hypothesis new ag mass fractions and cu ag ratios in different groups of martian meteorites are presented and compared with data from chondrites and samples from the earth s mantle silver contents in lherzolitic olivine phyric and basaltic shergottites and nakhlites range between 1 9 and 12 3 ng g the data display a negative trend with mgo content and correlate positively with cu contents in spite of displaying variable initial 143 nd values and representing a diverse spectrum of magmatic evolution and physiochemical conditions shergottites and nakhlites display limited variations of cu ag ratios 1080 320 1 s n 14 the relatively constant cu ag suggests limited fractionation of ag from cu during the formation and evolution of the parent magmas irrespectively of whether sulfide saturation was attained or not the mean cu ag ratio of martian meteorites thus reflects that of the martian mantle and constrains its ag content to 1 9 0 7 ng g 1 s carbonaceous and enstatite chondrites display a limited range of cu ag ratios of mostly 500 2400 ordinary chondrites show a larger scatter of cu ag up to 4500 which may have been caused by ag redistribution during parent body metamorphism the majority of chondrites have cu ag ratios indistinguishable from the martian mantle value indicating that martian core formation strongly depleted cu and ag contents but probably did not significantly change the cu ag ratio of the mantle compared to bulk mars bulk mars is richer in moderately volatile elements than earth however the martian mantle displays a much stronger depletion of the moderately volatile elements cu and ag e g by a factor of 15 for cu this observation is consistent with experimental studies suggesting that core formation at low p t conditions on mars led to more siderophile behavior of cu and ag than at high p t conditions as proposed for earth in contrast cu ag ratios of the mantles of mars and earth cu ag earth 3500 1000 display only a difference by a factor of 3 which implies restricted fractionation of cu and ag even at high p t conditions the concentration data support the notion that siderophile element partitioning during planetary core formation scales with the size of the planetary body which is particularly important for the differentiation of large terrestrial planets such as earth collectively the ag and cu data on magmatic products from the mantles of mars and earth and the data on chondrites confirm experimental predictions and support the limited fractionation of cu and ag during planetary core formation and high temperature magmatic evolution and probably also in early solar nebular processes

establishing a first archaeointensity record for the sw pacific abstract the dearth of archaeomagnetic intensity data from the southern hemisphere is a limiting factor in evaluating models of global geomagnetic field evolution during the holocene here we present high quality microwave archaeointensity data obtained from 34 ceramic fragments 21 archaeological contexts from the duke of york islands fiji and vanuatu sw pacific complementary thellier type experiments corrected for anisotropy give good agreement with the microwave results the majority of the new data prior to 250 ad exhibit significantly lower intensity than predicted by current global field models cals3k 3 and arch3k for the region with an apparent intensity minimum at 250 bc reaching as low as 50 of the present day field strength between 400 ad and 1500 ad the data are broadly consistent with the global field models but with a 20 higher field between 1200 and 1400 ad these new results therefore imply that the geomagnetic field has a greater range of variability than predicted and that further data from the region are essential to better constrain the global field models the results also demonstrate that establishing an archaeomagnetic reference curve for dating sw pacific ceramic artefacts is feasible which has potentially significant implications for pacific archaeological research

a comparison of a quasi perpendicular method of absolute palaeointensity determination with other thermal and microwave techniques abstract we describe test and explain the relative effectiveness of six thermal and microwave techniques of absolute palaeointensity determination applied to lava samples from mount etna sicily that acquired their thermoremanence trm in a known geomagnetic field the application of a single alternating field demagnetisation treatment prior to each measurement in a standard thellier experiment is demonstrated to be beneficial increasing the quality of the results and making the analysis simpler a new quasi perpendicular qp method dramatically improves the linearity of arai plots by reducing or altogether eliminating non ideal effects due to multidomain md grains two broad types of sample were encountered by this study and the qp method is the only one capable of producing accurate measurements from them both its ease of use speed and increased reliability should allow it to replace standard double heating methods in studies such as these where laboratory alteration can be detected by other means than ptrm checks the results of experiments performed using a microwave palaeointensity system provide further proof that the microwave de magnetisation process is equivalent to conventional thermal excitation they also demonstrate that microwave experiments are subject to the same risks as conventional experiments when performed on samples containing md grains the behaviour of the samples in both the thermal and microwave experiments is in good agreement with a recently proposed model of md trm which is based on first order symmetry of the remagnetisation process

metallic minerals thermal histories and parent bodies of some xenolithic ordinary chondrite meteorites we have studied metal grains in the hosts and lithic fragments of widely differing petrologic types in four xenolithic chondrftes using reflected light microscopy and electron probe analysis in weston and fayetteville which both contain solar flare tracks and solar wind gases kamacite taenite and tetrataenite ordered feni and troilite show a variety of textures on a wood plot of central ni content vs dimension taenite analyses scatter as if metal grains cooled at rates of 10 1000 and 1 100 k myr respectively through 700 k although metal in an h6 clast in fayetteville plots coherently with a cooling rate of 50 k myr we propose that metal grains cooled at these rates in chondritic clasts at different locations before host and clasts were compacted and were not subsequently heated above 650 k we predict a similar history for all gas rich ordinary chondrites by contrast metallic minerals throughout bhola and mezo madaras show more uniform textures and plot coherently giving cooling rates in the range 750 to 600 k of 0 1 and 1 k myr respectively we conclude that host and xenoliths in both chondrites were slowly cooled after compaction thus clasts in these chondrites experienced peak metamorphic temperatures and slow cooling through 700 k in different environments according to the conventional onion shell model for h l or ll chondrite parent bodies material of petrologic types 3 5 was arranged in successive shells around a type 6 core prior to catastrophic collisions which mixed all types intimately but if peak metamorphic temperatures were reached during not after accretion as seems plausible maximum metamorphism may have occurred in planetesimals 10 km in radius cooling through 700 k may then have occurred in larger bodies that accreted from these planetesimals iron meteorites mesosiderites and some achondrites may also have experienced melting in planetesimals and slow cooling in larger bodies

ordinary chondrites multivariate statistical analysis of trace element contents abstract we used standard multivariate discriminant functions borrowed from linear discriminant analysis and logistic regression to compare contents of mobile trace elements co au sb ga se rb cs te bi ag in tl zn cd in various populations of l4 6 or h4 6 chondrites to aid in our analysis we developed a non standard randomization simulation method that permits probability assignments on a distribution free basis because the sample database for antarctic l4 6 chondrites is very limited we could not establish that mildly and strongly shocked

antarctic and non antarctic meteorites form different populations compared with non antarctic falls antarctic meteorites include many of hitherto rare unique or unknown type1 such as lunar and putative martian samples2 4 attention has not previously been paid to the more common sorts of antarctic meteorites and here we focus on the most frequently encountered h5 chondrites we find that compositional differences between antarctic and non antarctic specimens of this class especially those involving thermally sensitive trace and ultra trace elements are so substantial that it seems extremely doubtful that the two sample populations are derived from the same parent population this implies that the contemporary falls less than 200 years old and the substantially older on average 300 000 years for victoria land antarctic meteorites either differ in genetic history or sample different extraterrestrial parent populations or both

chemical studies of h chondrites 4 new data and comparison of antarctic suites we report data for the trace elements au co sb ga rb ag se cs te zn cd bi tl and in ordered by putative volatility during nebular condensation and accretion determined by neutron activation analysis in 13 h5 chondriles from victoria land and 20 h4 6 chondrites from queen maud land antarctica these and earlier results provide antarctic sample suites of 34 chondrites from victoria land and 25 from queen maud land treatment of data for the most volatile 10 elements rb in in these suites by multivariate statistical techniques more robust as well as more conservative than conventional linear discriminant analysis and logistic regression demonstrates that compositions differ at marginally significant levels this difference cannot be explained by trivial terrestrial causes and becomes more significant despite the smaller size of the database when comparisons are limited to data from a single analyst and when all upper limits arc eliminated from consideration the victoria land and queen maud land suites have different mean terrestrial ages 300 kyr and 100 kyr respectively and age distributions suggesting that a time dependent variation of chondritic sources with different thermal histories is responsible as a result these two antarctic suites are on average chemically distinguishable from each other since h chondrites serve as a paradigm for other meteorite classes these results indicate that the near earth populations of planetary materials varied with time on the 105 year timescale

does thermal weakening explain basin inversion stochastic modelling of the thermal structure beneath sedimentary basins abstract the fact that basin inversion is possible long after the cessation of rifting indicates that at least some sedimentary basins are characterized by permanent relative weakness this paper investigates whether the steady state thermal structure in itself can provide the necessary pattern of rheological weakening to facilitate compressional inversion of a sedimentary basin by monte carlo simulation of a two dimensional thermal finite element model we find that generally the maximum moho temperature and therefore also the weakest upper mantle is encountered beneath the flanks of the basin the reason for this is heat refraction deviating away from the central parts of the sedimentary cover and into the adjacent basement highs the weakest crust however is located in the center of the basin due to sediment thermal blanketing lower confining pressure and the presence of relatively weak sediments

chemical studies of h chondrites 6 antarctic non antarctic compositional differences revisited we report data for the trace elements au co sb ga rb ag se cs te zn cd bi t1 and in ordered by putative volatility during nebular condensation and accretion determined by radiochemical neutron activation analysis of 14 additional h5 and h6 chondrite falls data for the 10 most volatile elements rb to in treated by the multivariate techniques of linear discriminant analysis and logistic regression in these and 44 other falls are compared with those of 59 h4 6 chondrites from antarctica various populations are tested by the multivariate techniques using the previously developed method of randomization simulation to assess significance levels an earlier conclusion based on fewer examples that h4 6 chondrite falls are compositionally distinguishable from the antarctic suite is verified by the additional data this distinctiveness is highly significant because of the presence of samples from victoria land in the antarctic population which differ compositionally from falls beyond any reasonable doubt however it cannot be proven unequivocally that falls and antarctic samples from queen maud land are compositionally distinguishable trivial causes e g analyst bias weathering cannot explain the victoria land antarctic non antarctic compositional difference for paradigmatic h4 6 chondrites this seems to reflect a time dependent variation of near earth meteoroid source regions differing in average thermal history

chemical studies of h chondrites ii weathering effects in the victoria land antarctic population and comparison of two antarctic populations with non antarctic falls abstract we report rnaa data for 14 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in sb se te tl u zn in interior portions of 45 different h4 6 chondrites 49 samples from victoria land antarctica and 5 h5 chondrites from the yamato mts antarctica relative to h5 chondrites of weathering types a and b all elements are depleted 10 at statistically significant levels in extensively weathered types b c and c samples probably by leaching on the ice sheet surface contents of 8 elements in extensively weathered samples may provide a qualitative ranking for terrestrial surface residence chondrites of weathering types a and b seem compositionally uncompromised and as useful as contemporary falls for trace element studies when data distributions for these 14 trace elements in non antarctic h chondrite falls and unpaired samples from victoria land and from the yamato mts queen maud land are compared statistically numerous significant differences are apparent concentrations of 8 elements differ significantly in the victoria land and non antarctic h5 chondrite populations essentially the same compositional differences and 53 mn content and shock history differences appear when h4 6 populations are compared contents of 8 elements differ when queen maud land and victoria land populations are compared and 5 for the queen maud land non antarctic comparison these and other differences give ample cause to doubt that the various sample populations derive from the same parent population the observed differences do not reflect weathering chance or other trivial causes a preterrestrial source must be responsible the least unlikely of these involves a temporal variation in the source regions from which meteoroids derive

the geomagnetic field intensity in new zealand palaeointensities from holocene lava flows of the tongariro volcanic centre very few absolute palaeointensity data exist from holocene aged rocks in new zealand here we present a new suite of high quality palaeointensities supported by detailed rock magnetic investigations samples from 23 sites representing 10 distinct eruptive units of the tongariro volcanic centre taupo volcanic zone new zealand were studied both traditional double heating and microwave palaeointensity methods were employed the reliability of the palaeointensity data varies with rock magnetic properties of the samples corresponding in particular to their positions within the lava flows the highest success rates are from samples obtained from near the flow tops where a significant proportion of the remanence unblocked at intermediate temperatures 200 350 c by contrast samples from flow centres particularly the parts showing platey fracturing have the lowest success rates reliable high quality palaeointensity results ranging from 32 4 5 1 t to 72 1 4 7 t were obtained from six flows with ages between c 12 800 yr bp and the present these correspond to virtual dipole moments that increase from 52 10 zam2 in the early holocene and peak at 112 14 zam2 about 300 yr ago the data agree well with calibrated relative palaeointensities from new zealand lake sediments the volcanic and sedimentary data together yield a holocene virtual axial dipole moment curve that fits the global average variation well in the early holocene but which differs significantly in recent millennia this difference is associated with recent migration of the southern high latitude core mantle boundary flux lobe towards new zealand as is seen in global field models less

cumberland falls chondritic inclusions ii trace element contents of forsterite chondrites and meteorites of similar redox state abstract mineralogic study of black inclusions in the cumberland falls enstatite achondrite revealed that they constitute a highly unequilibrated chondritic suite distinct from other chondrite groups this highly shocked suite the forsterite f chondrites exhibits mineralogic trends apparently produced during primary nebular condensation and accretion over a broad redox range we analyzed these samples and possibly related meteorites for ag as au bi cd co cs ga in rb sb se te tl u and zn trace elements known to yield important genetic information the results demonstrate the compositional coherence and distinctiveness of the f chondrite suite relative to other chondrites the antarctic aubrite alh a78113 may include more f chondrite material trace element contents do not vary with mineral compositions hence do not reflect redox variations during formation of f chondrite parental matter trace element mobilization during secondary heating episodes in the f chondrite parent or during its disruptive collision with the enstatite meteorite parent body is not detectable chemical trends in f chondrites apparently reflect primary nebular processes cosmochemical fractionation of lithophiles from siderophiles and chalcophiles occurred at moderately high temperatures certainly higher than those existing during formation of primitive carbonaceous enstatite and ordinary chondrites of petrologic type 3

mobile trace element contents in jilin chondrite abstract we determined ppm ppt levels of co se ga rb cs te bi ag in tl zn and cd arranged empirically in order of increasing mobility at 1000 c by radiochemical neutron activation analysis in eight jilin samples of known40ar content and a large vein from one of these the trace element contents of the vein do not differ markedly from those of jilin whole rock samples only rb correlates with40ar possibly due to chance all elements but cd are present at levels similar to those in h4 6 chondrites with longk ar age i e presumably mildly shocked these levels are low relative to those in analogous l4 6 chondrites suggesting that h chondrites formed and or evolved under higher pre shock temperatures than did mildly shocked l chondrites time temperature conditions during shock loading of jilin parent material were mild relative to those in strongly shocked l chondrites being sufficient at most only to mobilize cd

detecting multidomain magnetic grains in thellier palaeointensity experiments the thellier technique is the most commonly used method for absolute palaeointensity studies it is based on thellier s laws stating that partial thermoremanent magnetisations ptrms are independent and additive which however only are true for non interacting single domain sd grains for multidomain md grains individual ptrms are not independent and thellier palaeointensity experiments on rocks with a significant proportion of md grains may therefore lead to erroneous palaeofield estimates by introducing a ptrm tail check in the coe version of the thellier technique j geophys res 72 1967 3247 we present a simple method to detect and discard such rocks the usefulness of the ptrm tail check is exemplified by thellier palaeointensity experiments performed on two palaeomagnetic sample collections with different magnetomineralogy miocene baked sediments from french massif central are shown to be ideal for thellier studies with the remanent magnetisation residing in thermally stable sd grains for palaeocene eocene basaltic lavas from faeroe islands 64 of otherwise acceptable palaeointensity estimates are discarded due to the failure of ptrm tail checks indicating the presence of significant concentrations of md grains 2001 elsevier science b v all rights reserved

a test of the cosmogenic 3he production rate in the south west pacific 39 s calculation of surface exposure ages using in situ cosmogenic nuclides requires accurate knowledge of local production rates here we report the first attempt to calibrate cosmogenic 3he production in the south west pacific region we present a new radiocarbon chronology that precisely dates the emplacement of the murimotu formation a large debris avalanche deposit in central north island new zealand ca 830 m asl 39 s which occurred 10 4 10 6 cal ka bp measurements of cosmogenic 3he in pyroxene separated from large andesitic blocks exposed during this event yield a sea level high latitude production rate of 120 12 atoms g 1 a 1 lm scaling this is consistent with a recent global compilation comprised predominantly of calibration sites located in the northern hemisphere thus we conclude that the globally compiled cosmogenic 3he production rate is valid in the south west pacific using independent proximal calibrations of cosmogenic isotopes 10be and 14c from quartz in new zealand we derive cosmogenic 3he 10be and 3he 14c production ratios of 32 2 3 2 and 10 6 1 6 respectively

aubrites and diogenites trace element clues to their origin we have analyzed by rnaa 25 aubrite and 9 diogenite samples for 13 to 29 siderophile volatile and lithophile trace elements both meteorite classes show a typically igneous siderophile element pattern with ir os re ge more depleted than au ni pd sb but aubrites tend to have about 10 higher abundances 10 3 10 4 cl for the first 4 and 10 2 10 3 cl for the last 4 siderophiles apparently reflecting smaller metal silicate distribution coefficients at lowerf o2 or less complete segregation of metal se is surprisingly abundant in aubrites up to 0 4 cl but te is less so sete 5 cl apparently due to its stronger siderophile character other volatiles ag zn in cd bi t1 show depletions intermediate between lunar dunite and the earth s mantle of 7 aubrites analyzed for ree ce nd eu tb yb lu 6 are depleted in ree 0 08 0 5 cl and 5 show negative eu anomalies the exceptions are bishopville and mt egerton silicate this supports an igneous origin as already noted by boynton and schmitt 1972 no samples of the complementary basaltic and feldspathic rocks have been found thus far but one of our samples of khor temiki dark is a candidate for the basalt it is 5 7 enriched in ree and only slightly less so in rb cs and u though shocked and enriched in siderophiles to 0 05 cl it apparently represents a new meteorite class three diogenites analyzed for ree show very diverse patterns from strongly depleted in light ree for tatahouine ce 0 01 cl to flat for garland 2 5 cl the data confirm the trends found by fukuokaet al 1977 as well as their interpretations factor analysis shows several parallel groupings for aubrites and diogenites siderophiles re ir os pd ge chalcophiles se te volatiles ag in tl and incompatibles u ree and cs or rb but there are some differences for elements such as ni sb cd bi au and zn most of which behave more sensibly in aubrites than in diogenites several element pairs that differ greatly in volatility cs u ge ir correlate closely in aubrites in approximately cl chondrite proportions these correlations and other lines of evidence suggest strongly that aubrites originated by igneous processes in their parent body not by direct nebular condensation the source material may have resembled el chondrites in oxidation state and depletion of refractories metal and volatiles

importance of cooling rate dependence of thermoremanence in paleointensity determination 1 the practical effect of cooling rate on the magnitude of thermal remanent magnetization trm is experimentally tested using both natural and synthetic magnetites for synthetic and natural single domain sd magnetites trm intensity increases as the cooling rate decreases because a longer exposure time for slower cooling offers more chances to achieve an equilibrium magnetization multidomain md magnetites have the opposite response trm decreases as the cooling rate increases because slower cooling allows more time to achieve lower magnetization because of self demagnetization for pseudo single domain psd magnetite the effect of cooling rate on the remanence intensity appears to be insignificant intermediate in behavior between sd and md for a sd trm differences are restricted to lower temperatures but diminish near the curie point strongly indicating a serious problem in a conventional treatment of cooling rate correction on the practical side merely applying trm differences as a correction can overcorrect the true paleointensity another important significance of the present study is that a cooling rate difference alone can cause a slight nonlinearity in an arai plot for a sd

a geomagnetic field model for the holocene based on archaeomagnetic and lava flow data abstract we propose a new geomagnetic field model for the holocene period based on archaeomagnetic and lava flow data avoiding the use of lake sediment data the source of data comes from the geomagia50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 yr the model called sha dif 14k allows us to analyse the behaviour of the geomagnetic field for the last 14 000 yr from 12 000 bc to 1900 ad for the model construction we use the spherical harmonic analysis in space and the penalized cubic b splines in time both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core mantle boundary cmb to assure the convergence of the model for the last 3 ka the model predictions agree with those given by the global model arch3k 1 and the european model scha dif 3k for older epochs the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the holocene for the last 9 ka the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 bc and 3000 bc and the well known continuous decreasing trend of the geomagnetic field strength for the last millennium and a half a general view of the time average evolution of the geomagnetic field flux lobes at the cmb for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum this lobe vanishes when the dipolar field is decreasing the north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5 1 km yr and 3 7 km yr respectively the model shows that the geomagnetic field can be averaged as axial dipolar in 2000 yr within an error of 5 the typical uncertainty of the palaeomagnetic studies finally and following the recent definition of archaeomagnetic jerks we found 8 critical events in the time evolution of the geomagnetic field for the last 8 ka characterized by a maximum in the hemispheric asymmetry of the proposed model the model is available in the earth ref digital archive at http earthref org erda 1897

original structures and fragmentation and reassembly histories of asteroids evidence from meteorites abstract if chondritic meteorites were internally heated after accretion had ended then the hottest material would have been buried the deepest and should have cooled the slowest if this is correct there ought to be a correlation between cooling rate and petrographic type a measure of the extent to which chondrites were metamorphosed i e heated published and new cooling rates derived from the compositions of metallic iron nickel grains do not display this correlation implying either that chondrite parent asteroids never had onion shell structures or that bodies with onion shell structures were broken up and reassembled prior to cooling to below 500 c the temperature at which cooling rate information is recorded in metallic iron nickel chondritic regolith breccias formed from materials that resided on the surfaces of their parent asteroids metallic iron nickel grains in h and l chondrite regolith breccias indicate that the breccia constituents cooled at rates ranging from 1 to 1000 k myr based on thermal calculations these cooling rates suggest that the materials spread out on the surfaces of h and l chondrite parent asteroids originated at depths ranging from about one kilometer to several tens of kilometers craters deep enough to excavate tens of kilometers cannot form on typical asteroidal bodies only 100 to 300 km in diameter without disrupting them therefore it appears that at least some asteroids namely the parent bodies of h and l chondrites were disrupted after cooling to below 300 c and then reassembled to create surfaces containing rocks that originated at a wide range of depths these results support theoretical calculations suggesting that many asteroids were broken up and subsequently reassembled into gravitationally bound rubble piles

magnetic properties and paleointensities as function of depth in a hawaiian lava flow the outcome of paleointensity experiments largely depends on the rock magnetic properties of the samples to assess the relation between volcanic emplacement processes and rock magnetic properties we sampled a vertical transect in a 6 m thick inflated lava flow at hawaii emplaced in 588 ad its rock magnetic properties vary as function of distance from the flow top the observations can be correlated to the typical cooling rate profile for such a flow the top and to a lesser extent the bottom parts of the flow cooled faster and reveal a composition of tm60 in which the magnetic remanence is carried by fine grained titanomagnetites relatively rich in titanium with associated low curie and unblocking temperatures the titanomagnetite in the slower cooled central part of the flow is unmixed into the magnetite and ulvospinel end members as evidenced by scanning electron microscope observation the remanence is carried by coarse grained magnetite lamella tm0 with high curie and unblocking temperatures the calibrated pseudo thellier results that can be accepted yield an average paleointensity of 44 1 2 4 t this is in good agreement with the paleointensity results obtained using the thermal izzi thellier technique 41 6 7 4 t and a recently proposed record for hawaii we therefore suggest that the chance of obtaining a reliable paleointensity from a particular cooling unit can be increased by sampling lavas at multiple levels at different distances from the top of the flow combined with careful preliminary testing of the rock magnetic properties

a planetary h group pebble in the barwell l6 unshocked chondritic meteorite abstract one stone of the barwell l6 shower contains an igneous inclusion with the oxygen isotopic signature of h group chondrites the inclusion is composed dominantly of olivine with a composition fo 75 5 identical with that of its host other phases are only partially equilibrated with the host the inclusion has a fractionated rare earth element pattern showing depletion in the heavy rare earth elements and a positive eu anomaly it is depleted in siderophile elements inclusion and host have ar ar ages 4 44 and 4 51 ga respectively and 129 xe r i ratios identical within experimental error we conclude that melting occurred very early on an h group chondritic body two objects from a single meteorite have different oxygen isotopic ratios but identical 129 xe r 127 i ratios which may indicate that the i xe systematics reflect chronological differences in closure to xe rather than isotopically heterogeneous iodine the inclusion and its host cooled to xe closure temperature contemporaneously with chondrules from unequilibrated ordinary chondrites

chemical studies of h chondrites 9 volatile trace element composition and petrographic classification of equilibrated h chondrites to examine the thermal history of the parent body bodies of equilibrated h chondrites we treated data for 11 volatile trace elements co rb ag se cs te zn cd bi tl and in in order of putative volatility in 90 falls 15 h4 46 h5 and 29 h6 using univariate statistical tests contents of few of these elements differ significantly between any two of these suites one element cs differs systematically between all three pairs of suites co and tl differ between two pairs of suites for co and cs contents varied as h4 h5 h6 while for tl contents varied as h4 600 k with the suites deriving from a stratified parent body bodies

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

a new high resolution record of holocene geomagnetic secular variation from new zealand we present the first full holocene palaeomagnetic secular variation record from new zealand the 11 500 year long record from the sediments of mavora lakes comprises composite declination inclination and relative palaeointensity logs compiled from two six metre long cores and the uppermost 1 5 m of another an age model has been developed from 28 ams radiocarbon age determinations on fragments of southern beech lophozonia menziesii and fuscospora cliffortioides leaves the excellent between core correlation in all three components of the field results in a high resolution palaeosecular variation record with precise and accurate age control the variations change in character from high amplitude in phase declination and inclination swings in the earliest part of the record to low amplitude variations in the middle part and declination and inclination swings that are 90 out of phase leading to broad looping of the vector in the upper part of the record that is consistent with westward drifting sources in the outer core the present day field at the site dec 24 2 e inc 70 7 f 59 t represents a rare steep and easterly extreme direction but close to average intensity the palaeointensity is inferred to have varied between about 40 and 90 t with variations that to some extent mirror variations in the virtual axial geomagnetic dipole moment seen from global data but also show some notable differences particularly in the past few thousand years

unequilibrated ordinary chondrites a tentative subclassification based on volatile element content for unequilibrated ordinary chondrites uoc two measures of primitiveness are available volatile content in principle reflecting accretion conditions from the solar nebula and metamorphism reflecting reheating in the parent bodies these two measures do not always correlate and we have therefore developed a tentative classification scheme based on volatile content that complements the searset al 1980 scheme based on metamorphism like the latter it subdivides type 3 chondrites on a scale of 3 0 to 3 9 the notation 3 4 0 indicates a meteorite that is subtype 3 4 according to metamorphism and 3 0 according to volatile content the classification is based mainly on c and xe two elements that are little affected by shock induced reheating and to a lesser extent on ar36 bi in and tl of 22 meteorites considered the majority have concordant classifications 0 2 on the two scales however 5 meteorites are richer in volatiles than their metamorphic grade indicates sharps 3 4 0 alha 77011 3 5 0 ngawi 3 6 3 alha 77299 3 7 4 and mezo madaras 3 7 3 it remains to be seen whether these differences indeed denote a more primitive nature some new clues to the formation of chondrites may eventually come from xe and c their concentrations in uoc s vary by more than 5 but the xec ratio remains nearly constant at 3 4 10 3 of the solar system ratio even the ratios for other chondrite classes differ only slightly from that for uoc s e g c3o 1 5 and e3 4 0 4 either the 4 factors determining this ratio t t p and internal surface area of the carbon varied in complementary fashion or more probably they varied only slightly in the entire source region of chondrites

chemical studies of h chondrites iii regolith evolution of the fayetteville chondrite parent abstract data for ag au bi cd co cs ga in rb sb se te tl and zn in consortium samples of solar gas and track rich dark matrix and dark and light clasts in the fayetteville h chondrite regolith breccia were determined by radiochemical neutron activation analysis the matrix proved chemically homogeneous at a level never before observed in an ordinary chondrite most dark clasts had similar mean trace element concentrations as matrix but were compositionally much more heterogeneous two clasts were unusual one having apparently formed from impact melted soil the other representing a mixture of 90 matrix 10 c2m chondrite the single light clast proved compositionally similar to h4 6 chondrite falls except for its higher contents of labile bi cd in and tl relative to matrix all other samples seemed cs deficient other h chondrite regolith breccias studied in the past had shown peculiar cs and or rb contents so that these alkalis seem diagnostic of such breccias dark portions of such breccias apparently represent compacted regolith soil produced by isochemical comminution of normal dark and light clasts the dark clasts in turn likely represent primordial nebular condensate although it is possible that they represent planetary cold traps that garnered labile elements generated elsewhere in the parent body

thermoluminescence and the shock and reheating history of meteorites iv the induced tl properties of type 4 6 ordinary chondrites abstract the induced thermoluminescence tl properties of 121 equilibrated ordinary chondrites have been measured the samples were 74 h and 47 l chondrites of which 33 h and 32 l were from antarctica the distribution of tl sensitivities for non antarctic l chondrites differs from that of non antarctic h chondrites consistent with a greater proportion of the former class suffering post metamorphic shock data on the effect of laboratory annealing on tl sensitivity and step wise ar release measurements enable the meteorites to be sorted into three shock related temperature groups

cosmic ray constancy and cosmogenic production rates in short lived chondrites abstract five chondrites with short cosmic ray exposure ages 26al and 53mn saturation values deduced from short lived chondrites alone agree within 20 with those deduced from all chondrites values of 21p based on 53mn and 26al are 0 30 0 03 and 0 46 0 05 respectively in h chondrites possible causes for the difference include half life errors data selection and a recent 2 5myr increase in the cosmic ray intensity

variations in the geomagnetic dipole moment during the holocene and the past 50 kyr all absolute paleointensity data published in peer reviewed journals were recently compiled in the geomacia50 database based on the information in geomagia50 we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr with a focus on the holocene period a running window approach is used to determine the axial dipole moment that provides the optimal least squares fit to the paleointensity data whereas associated error estimates are constrained using a bootstrap procedure we subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment including those based on cosmogenic radionuclides be 10 and c 14 this comparison generally lends support to the axial dipole moments obtained in this study our reconstruction shows that the evolution of the dipole moment was highly dynamic and the recently observed rates of change 5 per century do not appear unique we observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non dipole field this study also shows that the holocene geomagnetic dipole moment was high compared to that of the preceding similar to 40 kyr and that similar to 4 10 22 am 2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur c 2008 elsevier b v all rights reserved less

magnetic field intensity study of the 1960 kilauea lava flow hawaii using the microwave palaeointensity technique summary it is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known in this study two vertical sections 16 m apart have been sampled from the approximately 1 m thick 1960 kilauea lava flow hawaii variations are seen in the rock magnetic and palaeomagnetic properties between and within the two sections indicating that there are small scale lateral and vertical variations in the lava flow the two sections showed dierent responses to microwave palaeointensity analysis section h6001 generally gave ideal linear behaviour on plots of natural remanent magnetization nrm lost against microwave induced thermoremanent magnetization t m rm gained whilst the majority of samples from h6002 showed anomalous two slope behaviour when all plots were interpreted by taking the best fitting line through all points the flow mean intensity for h6001 was 31 6 3 6 mt and that for h6002 was 37 1 6 4 mt compared with the expected intensity of 36 mt additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava and whether it is best to always interpret nrm lost t m rm gained plots by taking the line of best fit regardless of shape

chemical studies of l chondrites iv antarctic non antarctic comparisons abstract we report shock facies and rnaa data for 13 siderophile lithophile and chalcophile volatile mobile trace elements ag au bi cd co cs ga in rb se te tl zn in interior portions of 19 different l3 6 chondrites from victoria land antartica comparison of these data for essentially unweathered antarctic samples with those previously published for 39 l4 6 chondrite falls indicate substantial differences the victoria land population lacks the most heavily shocked 35 gpa representatives found in the non antarctic population while contents of nearly all trace elements studied are lower at statistically significant levels in strongly shocked 22 gpa falls than in mildly shocked 22 gpa ones this is not true for the victoria land population contents of most trace elements vary with petrologic type of heavily shocked facies d 22 35 gpa l chondrites from victoria land such a variation is not observed for non antarctic falls or mildly shocked samples of either population l4 6 chondrites from victoria land contain significantly lesser amounts of nearly every trace element than do falls these differences are reflected in correlations between elements including the putative cosmothermometric trace elements bi in and tl while antarctic weathering could account for the compositional differences between antarctic and non antarctic l chondrites such processes cannot be responsible for the shock differences observed physical and chemical differences between other sorts of antarctic and non antarctic meteorites suggest rather that the l chondrite differences are preterrestrial in origin if so the parent region s for the victoria land samples that fell to earth 0 1 to 1 myr ago generally formed and or evolved under higher temperature conditions than those regions yielding contemporary falls the dominant influence of late shock that altered mobile trace element contents of l chondrites falls is not evident in samples from victoria land

palaeointensity study of the hawaiian 1960 lava implications for possible causes of erroneously high intensities summary it is known that the hawaiian 1960 lava sometimes yields higher palaeointensities than the igrf 36 2 t in order to clarify the causes we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava according to various rock magnetic analyses they are classified into three groups with degrees of the deuteric oxidation in coe s version of the thellier method a significantly larger mean palaeointensity of 49 0 9 6 t n 17 was observed similar to previous studies these palaeointensities showed a dependence on the oxidation indices which can be explained by thermochemical remanent magnetization tcrm acquisition during the natural cooling stage of the lava although it is generally difficult to distinguish the tcrm from thermoremanent magnetization trm a lowtemperature demagnetization ltd treatment on nrm and trm in the thellier experiment seems to allow us to detect the influence of the tcrm on nrm another possible tool for tcrm detection is the double heating technique dht of the shaw method combined with ltd ltd dht shaw method it gave a better average of 39 4 7 9 t n 9 though the success rate was much lower most of the inappropriate results were screened by a combination of the double heating test the arm correction and the ltd treatment if two outliers are further excluded the average is improved to be 35 7 3 3 t n 7 which agrees well with the expected intensity the results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow

chemical studies of h chondrites 11 cosmogenic radionuclides in falls 1 we measured the long lived cosmogenic radionuclides 10be 26al and 36cl in 47 h chondrite falls 13 cluster 1 members 9 cluster 5 members and 25 random falls from the date and time of fall clusters 1 and 5 were previously identified as possible coorbital meteoroid streams with distinctive thermal histories being confirmed by contents of volatile trace elements here we use model data including a three radionuclide plot 10bebulk 26albulk versus 36clmetal 26albulk and the multivariate statistical techniques of logistic regression and linear discriminant analysis to compare radionuclide levels and their utility to differentiate specific suites from other h chondrites from our radionuclide results and from noble gas data from other workers we identified 35 falls with simple irradiation histories and cosmic ray exposure ages 4 ma eight others exhibit evidence for shorter 4 ma exposure three of which had complex exposure histories two having been reported by others previously three others may have had such a history in any event the small proportion of h chondrite falls with complex exposure histories supports recent suggestions that they are not commonly encountered as earlier workers suggested although cosmogenic radionuclides do not differentiate between cluster 1 and a random set of h chondrites h chondrites that lost 3he from solar heating are distinguishable from those with normal 3he levels

new palaeointensity data from holocene icelandic lavas we present rock magnetic and palaeointensity data from holocene icelandic lava flows including historical and pre historical lavas susceptibility versus temperature measurements indicate that the magnetic mineralogy is dominated by primary titanomagnetite that have experienced variable degrees of high temperature oxidisation the analyses also demonstrate that virtually all studied samples are thermally stable up to their curie temperatures thellier palaeointensity experiments were carried out on 89 samples from fourteen different lava flows spanning the age of 167 to 9450 cal years bp microwave thellier experiments were used for one third of the samples while conventional thermal thellier was used for the remainder the two methods produced similar palaeointensities altogether reliable absolute palaeointensity estimates were obtained from all of the lava flows with values ranging from 38 2 5 0 mu t to 117 9 8 3 mu t the new results indicate that the holocene geomagnetic field intensity was more dynamic than suggested by the current field models possibly including brief intervals of anomalously high field strength c 2011 elsevier b v all rights reserved less