The solar wind (SW) concentrator, a key instrument onboard the

Genesis mission, was designed to provide larger fluences of implanted SW

for precise isotope analyses of oxygen and nitrogen [1]. SW ions in the mass

range 4–28 amu were accelerated and focused on a “concentrator target” by

an electrostatic mirror. This concentration process caused some instrumental

mass fractionation of the implanted SW ions as function of the radial position

on the target. Correction of this fractionation will be based on a combination

of the measured radial fractionation of Ne isotopes with results of simulations

of the implantation process using the actual performance of the concentrator

and the SW conditions during exposure. Here we present He and Ne

abundance and Ne isotopic composition data along one arm of the gold cross

that framed the 4 concentrator subtargets

Allton, J.

Bastien, R.

Burnett, D.

Hohenberg, C. M.

Mabry, J. C.

Marrocchi, Y.

McNamara, K.

Meshik, A. P.

Pravdivtseva, O. V.

Stansbery, E.

Here we report Ar results from the aluminum on sapphire (AloS) bulk regime samples, from which Ne results were obtained [1]. Ar measurements from other regimes are in progress

Caltech Authors - Main

69th Meeting of the Meteoritical Society: Abstracts A109 
5273 
Rb-Sr ISOTOPE DATA FOR CORE SAMPLES OF THE ICDP 
BOSUMTWI SCIENTIFIC DRILLING PROJECT, GHANA 
S. Luetke1• 2, A. Deutsch1• 2, and A. Sokol1. 1Institut flir Planetologie, 
Universitat Munster, Wilhelm-Klemm-Str. I 0, DE-48149 Muenster, 
Germany. 2ZLG, Mtinster, Germany. E-mail: luetke.s@uni-muenster.de 
Introduction: The 1.07 Ma old Bosumtwi impact structure, Ghana 
(06°32'N, 0 I 0 25'W) is a young and excellent preserved complex crater. As 
part of the Bosumtwi Core Drilling Project (BCDP) two cores were drilled 
into impactites (BCDP-7 A: annular moat, BCDP-8A: central uplift). In 
contrast to the broad spectrum of target and impact lithologies found on the 
crater rim, the drill cores mainly consist of meta-greywackes, phyllites and 
impact breccias [I, 2]. The goal of this isotope study is to constrain the 
precursor lithologies of Bosumtwi-related impact glasses (Ivory Coast 
tektites [IVC] and microtektites). 
Samples: We investigated I) six breccias of cores 7 A and 8A, 2) two 
meta-greywackes (7A), and 3) two shales (7 A). (I) consist of mineral (mainly 
quartz, feldspar, and calcite) and lithic fragments (meta-greywacke and a 
variety of shales to phyllite) ranging in diameter from 0.1 to I 0 cm. The fine 
grained matrix additionally contains sheet silicates. To estimate the influence 
of clasts to the whole rock isotope systematics different parts of breccias were 
separated, i.e., (i) domains exclusively consisting of matrix and clasts :o;0.5 
cm, (ii) such with matrix and clasts mainly larger than 1 cm, and (iii) single 
large meta-greywacke clasts (:2:5 cm). (2) one meta-greywacke is medium 
grained, the other one phyllitic; (3) the shales are grey to dark grey, very fine 
grained, and display a foliation; they have a powdery consistence. 
Rb-Sr Isotope Data: The breccias from core 8A have 87Sr/86Sr ratios 
between 0.703350 ± 14 (2cr) and 0.708955 ± 12, those of core 7A higher 
values from 0.720310 ± 13 to 0.72581 ± 10. The breccia domains (i), (ii), and 
(iii) don't display large variation indicating the absence of not yet sampled 
target lithologies (e.g., granitoids) in the matrix. Two shales of 7 A show 
much higher present day 87Sr/86Sr ratios (0.728310 ± 13 and 0.750205 ± 14) 
which is within the range published by [3] for shales, greywackes, and 
phyllites collected at the rim and in the vicinity of the crater. Reflecting the 
lower content of micas, greywackes of core 7 A yield relatively low 87Sr/86Sr 
ratios (0.716423 ± 14 and 0.718968 ± 14), in accordance with our earlier 
results of core 8A [4]. Respective regression line calculations using the 
different lithologies result in rather low initial 87Sr/86Sr ratios of0.7107 (7A) 
and 0.7027 (8A); the correspondent age values do not date a so far 
documented event, their geological relevance is questionable. 
Outlook: The current set of isotope data does not allow to correlate 
specific target rocks with IVC. Therefore further isotope studies (Rb-Sr, Sm-
Nd) as well as SEM analyses are in progress. 
Acknowledgements: We appreciate support by DFG grant De 401/19. 
Skillful technical assistance was given by H. Baier, U. Heitmann, and 
V. Heinrich. 
References: [l] Reimold W. U. et al. 2006. Abstract #1350. 37th Lunar 
and Planetary Science Conference. [2] Deutsch A. et al. 2006. Abstract 
#1292. 37th Lunar and Planetary Science Conference. [3] Koeberl C. et al. 
1998. Geochimica et Cosmochimica Acta 62:2179-2196. [4] Luetke S. et al. 
2006. Abstract# 1811. 3 7th Lunar and Planetary Science Conference. 
5287 
ARGON AND NEON IN GENESIS ALUMINUM-COATED 
SAPPHIRE COLLECTORS FROM REGIME ARRAYS 
J. C. Mabry1, A. P. Meshik1, C. M. Hohenberg1, Y. Marrocchi1, 0. V. 
Pravdivtseva1, J. Allton2, R. Bastien2, K. McNamara3, E. Stansbery3, and D. 
Bumett4• 1Washington University, Physics Department, St. Louis, Missouri 
63130, USA. E-mail: jcmabry@wustl.edu. 2Lockheed Martin c/o NASA/ 
JSC, Mail Code KT, Houston, Texas 77058, USA. 3NASA/JSC, Mail Code 
KA, Houston, Texas 77058, USA. 4Geology I 00-23, Caltech, Pasadena, 
California 91125, USA 
Introduction: Here we report Ar results from the aluminum on 
sapphire (AloS) bulk regime samples, from which Ne results were obtained 
[ 1]. Ar measurements from other regimes are in progress. 
Table 1. 
Regime 20Ne fluence, I 0 12/cm2 20Ne/22Ne 21 Ne/22Ne 
Bulk 1.23 ±.I I 13.96 ± .03 .0346 ± .003 
IS .352 ± .032 13.98 ± .04 .0340 ± .004 
CME .271 ± .024 13.93 ± .04 .0336 ± .004 
C-H .362 ± .032 13.94 ± .04 .0345 ± .004 
Method: Since elemental and isotopic abundances of light noble gases 
in solar wind differ substantially from terrestrial air (usually used for 
calibration), we used specially tailored calibration procedures. For Ar, we 
lowered the ion source emission to 50 µA, from our typical 150 µA. Using 
this procedure, mass discrimination was small and reproducible at less than 
0.3%/amu. 
The AloS samples were loaded into an extraction. cell specially 
designed to minimize Al sputtering effects, which can contribute 
significantly to the blank and block the viewport. We rastered areas of 4, 10, 
15, and 20 mm2 for Ar and 1-2 mm2 for Ne, using a Q-switched infrared 
laser, slightly defocused to optimize the surface energy density and the time 
needed to complete the raster. The corrections for 1 H3sc1+ and 1 H37Cl" 
interferences at A= 36 and 38 were negligible, as was the 40Ar blank (<5 x 
10-10 ccSTP) with observed 40 Ar/36 Ar ratios between 3 and 10. 
Ar fluences were calibrated using both an air standard and Springwater 
olivine grains (mg size), with known amounts ofspallogenic 36Ar, 38Ar, 21Ne, 
and 22Ne [2]. These two calibrations differed by about 8%, which should 
improve by ongoing interlab calibrations. 
Results: The Ar data from all four rastered areas formed a nearly 
perfect straight line when the ratios of 36 Ar/40 Ar versus 38 Ar/40 Ar were 
plotted, indicating a mixing of only two distinct components: solar wind and 
terrestrial atmosphere, no SEP or HCl effects. We calculated fluences (not 
corrected for backscatter) of(2.4 ± 0.2) x 1010 36Ar /cm-2 and (4.5 ± 0.4) x 
109 38 Ar/cm-2. All four of our 36 Ar/38 Ar ratios agree to within 5 permil. 
Table 2. 36Ar/38Ar ratios (from [3] and this work). 
Terrestrial air 
Apollo foils 
Lunar regolith (Zurich) 
Lunar regolith (Minnesota) 
SOHO/MTOF 
Regime bulk (this work, weighted average) 
5.32 
5.3 ± 0.3 
5.48 ± 0.05 
5.80 ± 0.06 
5.5 ± 0.6 
5.467 ± 0.010 
Acknowledgements: Supported by NASA grants NNJ04HI l 7G and 
NAG5- l 2885. 
References: [l] Hohcnberg C. M. et al. 2006. Abstract #2439. 37th 
Lunar and Planetary Science Conference. [2] Megrue G. H. 1968. Journal of 
Geophysical Research 7:2027-2033. [3] Weins R. C. et al. 2004. Earth and 
Planetary Science letters 222:697-712. 


English

Argon and neon in Genesis aluminum-coated sapphire collectors from regime arrays

Heber, V. S.

Wiens, R. C.

Olinger, C.

Burnett, D. S.

Baur, H.

Wiechert, U.

Wieler, R.

A72 69th Meeting of the Meteoritical Society: Abstracts
5199
FROM SIZE SORTING OF CHONDRULES TO ACCRETION OF
PARENT BODIES—THE EFFECTS OF PHOTOPHORESIS
H. Haack1, O. Krauss2, and G. Wurm2. 1Natural History Museum of
Denmark, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark. E-mail:
hh@snm.ku.dk. 2Institute for Planetology, Wilhelm-Klemm-Str 10, D48149
Münster, Germany
Introduction: Recent evidence based on 26Al chronology suggest that
the differentiated asteroids accreted ~0.7 Myr after CAI formation, while
chondrules were still forming in the nebula [1]. Chondrules appear to have
been size-sorted prior to accretion [2], suggesting that physical processes
allowed rapid accretion of some asteroids while components of other
asteroids formed and were being size-sorted at the same time. Observations
of asteroids and theoretical models suggest that the differentiated asteroids
formed closer to the Sun than primitive asteroids, possibly in the terrestrial
planet forming region [3]. We believe that several of these observations could
be attributed to photophoresis, which have recently been shown to be of
significance while gas and dust coexisted in the solar nebula [4].
Chondrule and CAI-Based Constraints: Several clues to the sorting
and concentration processes come from the observations of chondrules and
CAIs in chondrites. 1) Chondrules are better sorted than CAIs [5]. If the
sorting process was operating on a small scale we should expect that all of the
locally available components were equally well sorted. We thus infer that the
sorting process was operating on a large scale. 2) Chondrules are common in
all types of equilibrated chondrites whereas CAIs are only common in
carbonaceous chondrites, 3) CAIs apparently formed close to the Sun but are
mainly found in carbonaceous chondrites believed to originate in the outer
part of the asteroid belt. 4) Differences in oxygen isotope signatures show
that the source regions for ordinary, enstatite, and carbonaceous chondrites
were separated from each other in space and/or time.
Photophoresis and Size Sorting in the Nebula: We suggest that
photophoresis could have two significant effects on the particle motion in the
solar nebula. In the early stages while the nebula was still optically thick
photophoresis would help concentrate particles at the inner edge of the disk
leading to enhanced accretion rates here [6]. As the nebula became optically
thin photophoresis pushed chondrules and CAIs out to the point were inward
motion caused by gas drag is balanced by the outward motion caused by
photophoresis and radiation pressure. The particles will drift toward the
radial distance where the forces balance and since the photophoresis is a size
dependent force, different size ranges of chondrules and CAIs will
accumulate and subsequently accrete at different heliocentric distances. As
the gas gets thinner and thinner the accumulation point will move inward [7].
The first chondritic bodies will therefore accrete in the outer parts of the belt
and probably include the majority of the remaining CAIs. As the
accumulation point moves inward, later generations of chondrules will be
incorporated in chondrite parent bodies largely devoid of CAIs, in the inner
part of the asteroid belt.
References: [1] Bizzarro M. et al. 2005. The Astrophysical Journal
632:L41–L44. [2] Kuebler K. E. et al. 1999. Icarus 141:96–106. [3] Bottke
W. F. et al. 2006. Nature 439:821–824. [4] Wurm G. and Krauss O. 2006.
Icarus 180:487–495. [5] May C. et al. 1999. Abstract #1688. 30th Lunar and
Planetary Science Conference. [6] Wurm G. et al. 2006. Meteoritics &
Planetary Science 41. This issue. [7] Petit J.-M. et al. 2006. Abstract #1558.
37th Lunar and Planetary Science Conference. 
5314
MASS-FRACTIONATION INDUCED BY THE GENESIS SOLAR
WIND CONCENTRATOR: ANALYSIS OF NEON ISOTOPES BY UV
LASER ABLATION
V. S. Heber1, R. C. Wiens2, C. Olinger2, D. S. Burnett3, H. Baur1,
U. Wiechert4, and R. Wieler1. 1Isotope Geology, NW C85, ETH, CH-8092
Zürich, Switzerland. E-mail: heber@erdw.ethz.ch. 2LANL, Space and
Atmospheric Science, Los Alamos, New Mexico 87544, USA. 3CalTech,
JPL, Pasadena, California 91109, USA. 4AG Geochemie, FU Berlin, 12249
Berlin, Germany
The solar wind (SW) concentrator, a key instrument onboard the
Genesis mission, was designed to provide larger fluences of implanted SW
for precise isotope analyses of oxygen and nitrogen [1]. SW ions in the mass
range 4–28 amu were accelerated and focused on a “concentrator target” by
an electrostatic mirror. This concentration process caused some instrumental
mass fractionation of the implanted SW ions as function of the radial position
on the target. Correction of this fractionation will be based on a combination
of the measured radial fractionation of Ne isotopes with results of simulations
of the implantation process using the actual performance of the concentrator
and the SW conditions during exposure. Here we present He and Ne
abundance and Ne isotopic composition data along one arm of the gold cross
that framed the 4 concentrator subtargets.
He and Ne were released from pits ~120 µm in diameter by UV laser
ablation using a 248 nm Eximer laser [2]. In the first 34 analyses, He and Ne
were analyzed together at constant analytical conditions. In a second set of 16
analyses, He and Ne were separated to protect the mass spectrometer from
solar 3He. In total, 12 positions along the arm (30 mm long) were analyzed,
each with 1 to 6 single analyses. He and Ne abundances increase from the
edge (at 30 mm) towards the center of the concentrator cross, He from
5.3E+15 ions/cm2 (at 20.5 mm) to 1.8E+16 ions/cm2 (at 2.9 mm) and Ne
from 3.5E+12 ions/cm2 (at 29.4 mm) to 3.4E+13 ions/cm2 (at 1 mm). Thus,
the concentration factor increases by about a factor of 10, similar to expected
values from post-flight models for oxygen. Applying a simplified backscatter
correction measured and expected Ne abundances agree within 20%. The
measured Ne isotopes show a large mass fractionation as function of the
target radius. The 22Ne values (relative to SW 20Ne/22Ne of 13.75, [3]) range
from −19‰ (at 26 mm) to +40‰ (at 2.9 mm), reflecting a preferential
implantation of the heavier isotopes towards the center of the concentrator
target. Precision of the 20Ne/22Ne ratios, expressed as error of the mean, is on
average 4‰ (2σ) for the analyses in which He and Ne were not separated.
More work is needed to reduce the considerably larger scatter observed so far
in the analyses where He and Ne were separated. The obtained Ne isotope
fractionation curve resembles, in shape and extent of fractionation, the post-
flight modeled δ18O curve. The two curves are offset by about 10‰. This is
probably to be explained by the missing backscatter correction for the
measured Ne isotopes. At the conference we will compare measured Ne data
with simulated results of Ne implantation at SW conditions prevalent during
Genesis collection period.
References: [1] Wiens R. C. et al. 2003. Space Science Reviews 105:
601–625. [2] Heber V. S. et al. 2006. Abstract #2175. 37th Lunar and
Planetary Science Conference. [3] Grimberg A. et al. 2006. Abstract #1782.
37th Lunar and Planetary Science Conference.
