Journal of Geophysical Research: Planets
Supporting Information for
Magnetism of a Very Young Lunar Glass
Jennifer Buz1*, Benjamin P. Weiss1, Sonia M. Tikoo2,3, David L. Shuster2,3, Jérôme
Gattacceca4, Timothy L. Grove1
1Department
of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology,
Cambridge, MA 02139, USA, 2Department of Earth and Planetary Science, University of California,
Berkeley, CA 94720, USA., 3Berkeley Geochronology Center, Berkeley, CA 94709, USA, 4CNRS, AixMarseille University, CEREGE UM 34, Aix-en-Provence, France, *Now at: Division of Geological and
Planetary Sciences, California Institute of Technology, Pasadena, CA 91125
Contents of this file
Text S1 to S2
Figures S1 to S9
Tables S1 to S5
Additional Supporting Information (Files uploaded separately)
Dataset S1
Introduction
This supporting information provides additional details on hysteresis, VRM, PRM, geoand thermochronometry experiments. Demagnetization data for all samples are
included in the supplementary figures if not in the main text. Additional elucidating
figures and tables are also provided. Demagnetization data is provided in the
supplementary dataset.
1
Text S1. Rock Magnetism of 12017
1.1 Hysteresis
Hysteresis loops were measured on a single sample of each the 12017 basalt and glass
lithologies using a Princeton Instruments MicroMag vibrating sample magnetometer at
CEREGE, Aix-en-Provence, France. Hysteresis data are shown in Fig. S1. Magnetic
hysteresis parameters are reported in Tikoo et al [2012]. Using the hysteresis data with
the diamagnetic and paramagnetic contributions subtracted, we estimated the saturation
remanence, saturation magnetization, and coercivity. The ratios of saturation remanence
to saturation magnetization (Mrs/Ms) for basalt and glass are 5.05×10-3 and 3.89×10-3,
respectively. The mass normalized Ms are 0.14 Am2/kg and 0.68 Am2/kg for the basalt
and glass, respectively. The ratios of remanent coercive force to coercive force (Hcr/Hc)
are 17.5 and 5.67 for basalt and glass, respectively. Using these parameters as well as the
coercivity of remanence determined from back field IRM experiments, we find that both
lithologies are dominated by multidomain grains.
1.2 VRM
A possible source of magnetization for 12017 is viscous remanent magnetization (VRM)
from exposure to the Earth’s magnetic field for 40 years at ambient temperatures. To
estimate the possible contribution of VRM on the magnetization of the samples, we
placed basalt sample 13B in the Earth’s magnetic field for 2 weeks and we placed glass
sample 12B in an artificial bias field of 0.2 mT generated by a coil inside our shielded
room for 21 hours. Upon removal of the applied field, we acquired continuous
measurements of the magnetization of the samples as they viscously relaxed in our
shielded room (< 200 nT) over the following two weeks. To estimate lower and upper
bounds on the amount of possible VRM acquired since arrival on Earth, we fit both linear
and exponential curves to the VRM decay data, respectively (Fig. S2). We extrapolated
the acquired remanence out to 40 years (approximate residence time on Earth) and
subtracted the decay time from being in our shielded room (approximately 1 year).
Linear fits suggest that VRM can account for 1.95% and 0.5% of the basalt and glass
NRM, respectively, and 1.7% and 1.8% of the LC component. Exponential fits suggest
that VRM can account for 10% and 11% of the basalt and glass NRM, respectively, and
21% and 34% of the LC component. These are actually all upper limits since they
assume that the samples were stationary in the Earth’s field over the last 40 years.
1.3 PRM
It is possible that the glass or basalt could have acquired a shock remanent magnetization
(SRM) from a meteoroid impact. It is important to consider this because SRM is capable
of recording very short lived fields like putative impact-plasma generated fields
[Crawford and Schultz, 1999]. To assess this possibility, we imparted a laboratory
pressure remanent magnetization (PRM) (as an analog for SRM) on basalt sample 12A2
following the methods of Gattacceca et al. [2010]. We immersed sample 12A2 in
polyethilsiloxane fluid to facilitate hydrostatic pressurization. We then put the capsule
containing the sample and fluid into a nonmagnetic pressure cell and raised the pressure
to 1.8 GPa. While maintaining this pressure for a minimum of 1 minute, we applied a
field of 800 μT using a coil wrapped around the cell. The field was then turned off, the
1
pressure removed over the course of a minute, and the sample subjected to a full AF
demagnetization sequence. A comparison of demagnetization of PRM with NRM is
shown in Figs. S5 and S7. Almost all of the magnetization acquired via PRM was
removed in the first AF step (20 mT), suggesting that even the LC component is too hard
to be explained as an SRM.
Text S2. 40Ar/39Ar and cosmogenic 38Ar geochronology analytical details
Two basalt aliquots of 12017 and a single aliquot of 12017 impact glass were
sequentially degassed to conduct 40Ar/39Ar geochronometry at the Berkeley
Geochronology Center following previously published procedures [Shea et al., 2012;
Shuster et al., 2010]. The basalt samples were placed into aluminum discs alongside
Hb3gr neutron fluence monitors and were irradiated for 100 hours, and the glass aliquot
was irradiated for 1 hour alongside ACs fluence monitors, at the Oregon State University
TRIGA reactor in the Cadmium-Lined In-Core Irradiation Tube (CLICIT) facility. After
irradiation, aliquots (~1 mg) of the irradiated basalt and glass were placed into small
metal tubes of high purity Pt-Ir alloy and incrementally degassed using feedbackcontrolled laser heating with a 30 W diode laser (wavelength of 810 ± 10 nm) equipped
with a coaxially aligned optical pyrometer. The single-color pyrometer was calibrated
against a type-K thermocouple under high vacuum (<10-8 torr) and under the same
conditions as the degassing analyses to correct for the temperature dependent emissivity
of the Pt-Ir tubes.
During sequential degassing, the samples were first held under static vacuum at a
controlled temperature to within ± 10°C for 600 s (Table S1). The extracted Ar was then
purified using one hot and one cold SAES® GP-50 getter pump fitted with C-50 cartridge
(St101 alloy). All five isotopes of Ar were analyzed with a Mass Analyzer Products 215c
mass spectrometer using a single Balzers SEV-217 discrete dynode electron multiplier.
Corrections for interfering nuclear reaction products [Renne et al., 2005], 37Ar and 39Ar
decay, spectrometer discrimination, and extraction line blanks were applied to the
measured signals. Apparent 40Ar/39Ar ages were calculated relative to the Hb3gr standard
(1081 Ma) or the ACs standard (1.206 Ma) using the decay constants and standard
calibration of Renne et al. [2011], and isotope abundances of Steiger and Jäger [1977];
corrections for trapped or cosmogenic 40Ar were not applied. The apparent cosmogenic
38
Ar exposure ages of each degassing step were calculated from the ratio of cosmogenic
38
Ar to reactor-produced 37Ar and 39Ar following the procedures described in Shuster and
Cassata [2015] and using the 38Ar production rate from Ca [Turner, 1971]. In this case,
the production of 38Arcos from Ti, Cr, Mn, Fe, and Ni was ignored; therefore, calculated
exposure ages represent upper bounds on the true surface exposure. Full datasets,
isotopic corrections, neutron irradiation parameters, and calculated step ages (both
40
Ar/39Ar and cosmogenic 38Ar) for the whole-rock and glass aliquots appear in Table S1.
For the analysis of impact glass, extractions that yielded Ar abundances below the
detection limit are excluded for clarity. The whole-rock analyses are shown as release
spectra, along with the apparent Ca/K ratios, in Fig. 7.
2
Figure S1. Hysteresis data for 12017. A) Basalt subsample 12A2. B) Glass subsample
12B. Large plots at left show hysteresis loops corrected for high-field (0.95-1 T)
paramagnetic slope while the smaller plots at right show the uncorrected data.
3
Figure S2. VRM decay experiments for 12017. (A) Basalt subsample 13B1. (B) Glass
subsample 12B. Black lines indicate exponential fits while red lines indicate linear fits.
4
5
Figure S3. Subsampling and orientation of 12017. A) Whole rock 12017 prior to
subdivision at Johnson Space Center (JSC). Underlying basalt is light gray and glass
splatter is shiny black. Approximate locations of subsamples used in this study are
indicated. NASA photo S70-44098. B) Illustration of saw cuts made at JSC during
sample processing, adapted from Lunar Sample Compendium [Meyer, 2005]. We used
these drawings to reconstruct how our allocated subsamples were mutually oriented. C)
Orientation of final subsamples used in this study. Subsamples 12A1A, 12A1B, and 59B
were not used in this study. The JSC and MIT coordinate systems are shown with
unprimed and primed labels, respectively, in (B) and (C).
Figure S4. Geologic setting of 12017. A) Lunar Reconnaissance Orbiter Wide Angle
Camera (LROC-WAC) photograph of the Apollo 12 landing site. Selected craters and the
small mound where sample 12017 was thought to have been collected are labeled. B)
Astronaut photograph (AS12-46-6825HR) of small mound where sample 12017 was
retrieved (sample is not identifiable in the photograph). Scale bar is estimated from the
Apollo transcripts.
6
Figure S5. Petrographic constraints on cooling rate of 12017 basalt from Grove and
Walker [1977]. Early and late stage cooling of the 12017 basalt based on plagioclase
width and pyroxene density are 0.30°C/hr and 0.35°C/hr, respectively. See Fig. 1 for
examples of plagioclase and pyroxene.
7
Figure S6. More examples of AF demagnetization over the coercivity range of the LC
component. Shown is a two-dimensional projection of the NRM vectors during
progressive sanding stages. Solid symbols represent the end points of magnetization
projected onto the horizontal N-E planes, and open symbols represent projections onto
the vertical U-E planes. All samples except sample 13B show removal of one or more
LC components. Sample 59A likely has two LC components, indicated by the grey
arrows. Red symbols indicate moment measurement following final sanding of the
8
parent sample for each subsample show here and scaled in intensity to the mass of the
subsample relative to its parent sample. These directions differ from the AF 0 mT
measurements because of the additional subsampling that occurred prior to beginning AF
demagnetization.
Figure S7. Comparison of AF demagnetization behavior of the NRM to that of different
laboratory-induced magnetizations over the coercivity range of the LC component. (Left)
12A2 basalt subsample demagnetization normalized to the pre-AF moment. (Right) 12B
glass subsample demagnetization normalized to the pre-AF moment.
9
Figure S8. More examples of AF demagnetization of 12017 over the HC range. Shown
is a two-dimensional projection of the NRM vectors during progressive sanding stages.
Solid symbols represent the end points of magnetization projected onto the horizontal NE planes, and open symbols represent those projected onto the vertical U-E planes. Note
the lack of any consistent moment or directional changes with successive AF steps.
10
Figure S9. Comparison of AF demagnetization behavior for different magnetization
types over the coercivity range of the HC magnetization. (Left) 12A2 basalt subsample
normalized to the moments after demagnetization to 6.5 mT. (Right) 12B glass
subsample normalized to the moments after demagnetization to 8.5 mT.
11
12
Isotope abundances given in nanoamps (spectrometer sensitivity is ~1.4×10-14 mols/nA),
and corrected for 37Ar and 39Ar decay, half lives of 35.2 days and 269 years, respectively,
and for spectrometer discrimination per atomic mass unit of 1.004535 ± 0.002968.
Isotope sources calculated using the reactor constants in Renne et al. [1998], assuming
(38Ar/36Ar)cos = 1.54, (38Ar/36Ar)trap = 0.188, and (40Ar/36Ar)trap = 0.
No corrections were made for cosmogenic 40Ar. Ages calculated using the decay
constants and standard calibration of Renne et al. [2011] and isotope abundances of
Steiger and Jäger [1977] and calculated relative to Hb3gr fluence monitor (1081 Ma) and
relative to ACs fluence monitor (1.206 Ma), for basalt and glass, respectively.
J-Values are 0.0262509 ± 0.0002064 and 0.000272 ± 0.000008, for basalt and glass
respectively.
Corrections were made for reactor produced 38Ar and 36Ar in age calculations.
Average analytical blanks are: 40Ar = 0.015; 39Ar = 0.0001; 38Ar = 0.00002; 37Ar =
0.0001; 36Ar = 0.00007 (nanoamps).
Temperature was controlled with approximately ± 10 ºC precision and ± 10 ºC accuracy;
each heating duration was 600 seconds.
The apparent 38Ar exposure ages are calculated for production only from Ca and K, so
represent upper bounds.
Table S1. Argon Analytical Details.
#
Lithology
P
Ni
S
Fe
Total
1
Glass
0.16
0
0.11
16.53
16.80*
2
Glass
2.53
1.28
0.02
96.21
100.04
3
Glass
8.22
1.97
0.39
88.58
99.16
4
Glass
4.18
1.45
0.38
93.35
99.36
5
Glass
7.44
1.52
9.70
80.39
99.05
1
Basalt
0.01
0
0.25
98.99
99.25
2
Basalt
0.01
0
0.06
98.93
99.00
3
Basalt
0.02
0.79
0.01
97.58
98.40
4
Basalt
0.02
0.78
0.01
99.45
100.28
Note: The first column lists the spot number corresponding to Fig. 2, the second column
lists the lithology hosting the metal grain. The second through fourth columns contain the
concentrations in wt.% of P, Ni, S, and Fe, respectively. The fifth column contains the
sum the previous four columns. Measurements were acquired with a JEOL-JXA-8200 at
the Massachusetts Institute of Technology electron microprobe facility.
*The low mass percentage total for this spot is likely due to the small size (<1 µm) of this
metal grain. The remaining majority of the mass is likely from Si and O from the
surrounding glass.
Table S2. Wavelength dispersive spectroscopy analyses of metal grains in 12017.
13
Sample
Basalt
12A
12A2
12A1C
13B*
Glass
12B
13A
13A1
13A2
59A**
Mass
(mg)
Type
Range
(mT)
N
Dec (°)
Inc
(°)
503
183
Sanding
LC
HC
LC
HC
Sanding
LC
MC
HC
NRM-8.5
8.5-69
NRM-8.0
8.0-64
NRM-11.5
12.0-54.0
54-80
6
17
77
15
74
13
22
66
27
249
294.5
145.7
239.9
127.0
135.6
263.8
121.0
144.9
-38.8
33.7
48.1
81.0
42.6
36.2
-17.4
-70.7
26.9
Sanding
LC
HC
Sanding
LC
HC
LC
HC
LC1
LC2***
HC
n/a
NRM-8.5
9-85
n/a
NRM-7
7.5-85
NRM-8.5
8.5-85
NRM-4.5
5.0-9.0
9.5-39
5
16
75
14
13
106
16
104
7
9
56
348.8
277.8
346.8
4.8
302.8
209
269.9
206.4
180
303.6
146.5
66.2
24.7
-65.1
-7.6
16.8
17.7
21.1
-78.6
-11.4
-3.9
74.6
104.3
131.6
27.1
132.9
69.9
49.5
15
DANG
(°)
127.1
74.26
151.6
132.1
124.6
146.6
91.01
133.7
38.5
129.7
159.6
106.2
52.51
91.63
110.9
114.5
MAD
(°)
27.2
12.0
37.1
11.0
35.3
23.3
36.3
35.4
34.0
24
9.8
31.8
27.2
6.1
34.9
14.0
30.0
9.4
15.8
45.5
Pass?
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Forced
?
No
No
Yes
No
Yes
No
No
No
Yes
No
No
Yes
No
No
Yes
No
Yes
No
No
Yes
Note: The first column contains sample and subsample names. Subsamples are listed as
indented sample names under their parent sample. The second column shows the mass of
each subsample. The third column designates whether the row describes the low
coercivity (LC), medium (MC), or high coercivity (HC) components of magnetization in
the sample. The fourth column contains the AF field values bounding the components
identified for each subsample. The fifth column shows the number of points (i.e., AF
steps) used in the PCA calculation for each component. Columns 6-9 show the mean
declination, mean inclination, DANG, and the MAD, respectively, for each component.
The tenth column indicates whether the component passed the DANG/MAD test. The
eleventh column indicates whether the component was forced through the origin during
the PCA calculation. *In Tikoo et al. [2012] sample 13B was referred to as sample 13b1.
**In Tikoo et al. [2012] sample 59A was referred to as sample 59. ***In Tikoo et al.
[2012] component LC2 was referred to as MC.
Table S3. NRM components.
Sample Starting Mass (mg)
Ending Mass (mg)
% Difference
12A
503.7
492.5
2.3
12B
32.2
29.7
7.7
13A
150.7
149.0
1.1
13B
167.2
152.1
9.0
Note: A ~20 mg flake of glass was chipped from 13B post-sanding.
Table S4. Mass changes throughout sanding.
14
Sample
Basalt
12A2
12A1C
Glass
12B
13A2
Comp
ARM slope
IRM
slope
0.05
mT
0.2 mT
0.6 mT
LC
2.71 ±
1.55
1.03 ±
0.19
0.45 ±
0.08
HC
0.13±
0.13
0.12 ±
0.06
LC
1.53 ±
0.64
HC
ARM paleointensity (μT)
IRM
0.05 mT
0.2 mT
0.6 mT
Paleoint
(μT)
0.057 ±
0.0062
101.1 ±
57.8
153.73
± 28.35
201.4 ±
35.82
171 ±
18.6
0.05 ±
0.03
0.0044
± 0.003
4.104 ±
4.85
16.41 ±
8.95
22.38 ±
13.43
13.2 ± 9
0.9 ±
0.13
0.5 ±
0.08
-
57.08 ±
23.88
134.32
± 19.40
223.88 ±
35.82
-
0.14 ±
0.17
0.08 ±
0.09
0.03 ±
0.06
-
5.223 ±
6.34
11.94 ±
13.43
13.43 ±
26.86
-
LC
3.93 ±
1.24
1.11 ±
0.11
0.33 ±
0.04
0.986 ±
0.11*
146.6 ±
46.26
165.67
± 16.41
147.76 ±
17.91
HC
0.17 ±
0.07
0.05 ±
0.02
0.02 ±
0.01
0.004 ±
0.001*
6.343 ±
2.61
7.46 ±
2.98
8.95 ±
4.47
13.03 ±
3.94
LC
0.85 ±
0.86
0.39 ±
0.19
0.14 ±
0.06
0.007 ±
0.003*
31.71 ±
32.08
58.20 ±
28.35
62.68 ±
26.86
22.05 ±
8.40
HC
0.24 ±
0.04
0.10 ±
0.01
0.04 ±
0.01
0.002 ±
0.0003*
8.955 ±
1.49
14.92 ±
1.49
17.91 ±
4.47
7.20 ±
0.99
295.8 ±
33.3
Note: The first column lists subsample numbers. The second column designates whether
the paleointensity experiment was conducted for the low coercivity (LC) component,
high coercivity (HC) component, or a magnetization component defined by AF steps of
23-85 mT in the sample. The third, fourth, and fifth columns show ΔNRM/ΔARM values
computed from paleointensity slope fits to the associated AF range using ARM
acquisition with 0.05 mT, 0.2 mT, and 0.6 mT DC bias fields, respectively. The sixth
column shows ΔNRM/ΔIRM values computed from paleointensity slope fits to the
associated AF range. All data reported are in the format slope ± 95% formal confidence
radius from Student’s t-test. The final four columns indicate the calculated paleointensity
using f’ = 1.34 and a = 3000. The first six columns are reproduced from Tikoo et al.
[2012]. The quoted uncertainties in the third through eight columns only represents that
associated with the linear regression and does not take into account systematic
uncertainties associated with the unknown values of a and f’. *Tikoo et al. [2012]
incorrectly reported IRM paleointensities for subsample 12B as belonging to 13A2. They
have been corrected here.
Table S5. Paleointensity Values.
Data Set S1. NRM AF Demagnetization data.
15
References
Crawford, D. A., and P. H. Schultz (1999), Electromagnetic properties of impactgenerated plasma, vapor and debris, Int. J. Impact Eng., 23, 169-180, doi:10.1016/S0734743X(99)00070-6.
Gattacceca, J., M. Boustie, L. Hood, J. P. Cuq-Lelandais, M. Fuller, N. Bezaeva, T. de
Resseguier, and L. Berthe (2010), Can the lunar crust be magnetized by shock:
Experimental groundtruth, Earth Planet. Sci. Lett., 299, 42-53,
doi:10.1016/j.epsl.2010.08.011.
Grove, T. L., and D. Walker (1977), Cooling histories of Apollo 15 quartz-normative
basalts, in Proceedings of the Eighth Lunar Science Conference, p. 1501-1520, Pergamon
Press, Inc., New York.
Meyer, C. (2005), Lunar sample compendium (online), 6,
<http://curator.jsc.nasa.gov/Lunar/lsc/index.cfm>.
Renne, P. R., G. Balco, K. R. Ludwig, R. Mundil, and K. Min (2011), Response to the
comment by WH Schwarz et al. on "Joint determination of 40K decay constants and
40
Ar/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar
geochronology", Geochim. Cosmochim. Acta, 75, 5097, doi:10.1016/j.gca.2011.06.021.
Renne, P. R., K. B. Knight, S. Nomade, K.-N. Leung, and T.-P. Lou (2005), Application
of deuteron-deuteron (D-D) fusion neutrons to 40Ar/39Ar geochronology, Applied
Radiation and Isotopes, 62, 25-32, doi:10.1016/j.apradiso.2004.06.004.
Renne, P. R., C. C. Swisher, A. L. Deino, D. B. Karner, T. L. Owens, and D. J. DePaolo
(1998), Intercalibration of standards, absolute ages and uncertainties in 40Ar/39Ar dating,
Chemical Geology, 145, 117-152, doi:10.1016/S0009-2541(97)00159-9.
Shea, E. K., B. P. Weiss, W. S. Cassata, D. L. Shuster, S. M. Tikoo, J. Gattacceca, T. L.
Grove, and M. D. Fuller (2012), A long-lived lunar core dynamo, Science, 335, 453-456,
doi:10.1126/science.1215359.
Shuster, D. L., G. Balco, W. S. Cassata, V. A. Fernandes, I. Garrick-Bethell, and B. P.
Weiss (2010), A record of impacts preserved in the lunar regolith, Earth Planet. Sci.
Lett., 290, 155-165, doi:10.1016/j.epsl.2009.12.016.
Shuster, D. L., and W. S. Cassata (2015), Paleotemperatures at the lunar surfaces from
open system behavior of cosmogenic 38Ar and radiogenic 40Ar, Geochim. Cosmochim.
Acta, 155, 154-171, doi:10.1016/j.gca.2015.01.037.
Steiger, R. H., and E. Jäger (1977), Subcommission on geochronology: convention on the
use of decay constants in geo-and cosmochronology, Earth Planet. Sci. Lett., 36, 359362, doi:10.1016/0012-821X(77)90060-7.
16
Tikoo, S. M., B. P. Weiss, J. Buz, E. A. Lima, E. K. Shea, G. Melo, and T. L. Grove
(2012), Magnetic fidelity of mare basalts and implications for a lunar dynamo, Earth
Planet. Sci. Lett., 337-338, 93-103, doi:10.1016/j.epsl.2012.05.024.
Turner, G. (1971), Argon 40- argon 39 dating: The optimization of irradiation
parameters, Earth Planet. Sci. Lett., 10, 227-234, doi:10.1016/0012-821X(71)90010-0.
17