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CRONUS Results: An interhemispheric Workshop
12/13 July 2008, Vancouver
Cl spallation production rate
calibration from Ca and K in lava flows
36
Irene Schimmelpfennig
CEREGE, France
Lucilla Benedetti
Raphaël Pik
Pete Burnard
Didier Bourlès
PH Blard
Alice Williams
Vincent Garreta
Silke Merchel
Bob Finkel
Jérôme Chmeleff
Tibor Dunai
Anne-S. Mériaux
Katja Ammon
Cosmogenic in-situ Cl
production mechanisms:
36
low e
• Slow negative muons: Capture by
Ca and K
36Cl
in situ
spallation
[ Cl]=(Ps + Pn + Pµ) texpo
36
al
la
tio
n
capture
lo
w
ne -e
ut ne
ro rg
ns y
slo
w
m
uo
ns
K Ca
epithermal) neutrons: Capture by 35Cl
sp
gy neutro
ns
Low-ener
fast neutrons
spallation
capture
ns
Fe
muo
Ti
slow
K Ca
35Cl
• Low-energy (thermal and
ner
elements Ca, K, (Ti, Fe)
fast neutrons
• Fast neutrons: Spallation of target
exposure
time
36
Ca:
Cl spallation production rates (SLHL)
Stone et al. 1996
Phillips et al. 2001
Swanson and Caffee 2001
40
%
48.8
dis
c
whole rock
re
separated minerals
pa
66.8
nc
whole rock
y
82
atoms 36Cl (g Ca)-1 a-1
K:
Evans et al. 1997
Phillips et al. 2001
Swanson and Caffee 2001
25
%
dis
c
162
sep. minerals
whole rock
re 137
pa
whole rock
nc
y
217
atoms 36Cl (g K)-1 a-1
I. Track 36Cl in whole rock and separated minerals
II. 36Cl production rate calibration for spallation of Ca and K
Calibration sites
Mt. Etna (Sicily, 38°N)
SI40+SI3
530m
K/Ar
33±2 ka
SO2
992m
SI41+SI29
825m
HF1
1748m
C
6±1 ka
14
SO3
783m
SO1
1204m
historic
0.4
ka
K/Ar
00
500
00
20
00
15
10
SI43
2007m
Payun-Matru
(Argentina, 36°S)
15±1 ka
K/Ar
10±3 ka
9 samples - trachybasalt:
Ca rich plagioclase
K/Ar
15±1 ka
PM06-31+32
2293m
PM06-26
2490m
PM06-20+21
2525m
2 samples - trachyte:
sanidine (K)
Tracking
Cl in whole rock and separated
minerals
Mt. Etna (Sicily, 38°N)
36
SI43:
• abundant Ca-plagioclase phenocrysts
• exposure age: 10±3 ka (K/Ar)
• 3He exposure age (pyroxene phenocrysts):
9.6±0.9 ka
SI40+SI3
530m
SO2
992m
SI41+SI29
825m
HF1
1748m
00
500
00
20
00
15
10
SI43
2007m
SO3
783m
SO1
1204m
Comparison:
Whole Rock and Plagioclase
Whole Rock
[atoms 36Cl g-1]
2.25x106
Plagioclase
2.17x106
measured
36
Cl
40%
1.25x106
Calculations
Gosse & Phillips 2001
1.50x106
9x
0.75x106
79%
low energy
neutron
calculated
36
capture
Cl by
35
Cl
19%
spallation
920 ppm Cltotal
calculation
How much 36Cl in
whole rock and
plagioclase?
PRCa Stone et al. 1996
PRK Evans et al. 1997
PRneutr Phillips et al. 2001
scaling Stone 2000
2.47x10
5
measured
36
Cl
2.33x105
calculated
92%
36
spallation
Cl
3 ppm Cltotal
Comparison:
Whole Rock and Plagioclase
Whole Rock
[atoms 36Cl g-1]
2.25x106
Plagioclase
2.17x106
40%
measured
36
Cl
1.25x106
Calculations
Gosse & Phillips 2001
1.50x106
9x
0.75x106
79%
low energy
neutron
calculated
36
capture
Cl by
35
Cl
19%
spallation
36
underestimation of
calculation
How much 36Cl in
whole rock and
plagioclase?
PRCa Stone et al. 1996
PRK Evans et al. 1997
PRneutr Phillips et al. 2001
scaling Stone 2000
2.47x10
5
measured
36
Cl
2.33x105
calculated
92%
36
spallation
Cl
Cl production ➡ complex behaviour of low-
920 ppm
Cltotalat land/atmosphere
3 ppm Cltotal
energy
neutrons
boundary
36
Cl production rate calibration for
spallation of Ca and K
Payun-Matru
Mt. Etna
Ca rich
plagioclase
sanidine (K)
[Ca] = 7.1 - 8.9%
[K] = 0.3 - 0.5%
[Cltotal] = 1-6 ppm
[Ca] = 0.6%
[K] = 5.4%
[Cltotal] = 8-13 ppm
3x106
6x106
2300m
825m
2x106
5301200m
1x106
atoms 36Cl g-1
atoms 36Cl g-1
2070m
4x106
2x106
1750m
0
0.4ka
6±1ka
10±3ka
33±2ka
0
15±1ka
Production rate determination
measured 36Cl
concentration
independent age
(+ radioactive decay
+ erosion)
chemical
composition
calculation
spallation production
rates from Ca and K
1 − exp−(λ36 +ρε/Λ )tindep
λ36 + ρε/Λ
?
?
correction factors:
scaling
thickness
shielding
geometry
sp
al
la
tio
n
lo
w
ne -e
ut ne
ro rg
ns y
slo
w
m
uo
ns
[36Cl]meas = (Fs ([Ca] PRCa + [K] PRK) + Fn Pn + Fµ Pµ) tindep
[ Cl]=(Ps + Pn + Pµ) texpo
36
Production rate determination
[36Cl]meas = (Fs ([Ca] PRCa + [K] PRK) + Fn Pn + Fµ Pµ) tindep
2 statistic methods:
1. “Best fit” linear model (least square)
1.5x105
1.0x105
0.5x10
5
PRCa = 50 ± 4
atoms 36Cl (g Ca)-1 a-1
36
36
Cl - B PRK - C
2.0x105
Cl - A PRCa - C
[36Cl]meas = A t PRCa + B t PRK + C t + Δ
0
0
1 000 2 000 3 000 4 000
A
6x105
4x105
PRK = 142 ± 5
2x105
atoms 36Cl (g K)-1 a-1
0
0
1 000 2 000 3 000 4 000
B
Production rate determination
[36Cl]meas = (Fs ([Ca] PRCa + [K] PRK) + Fn Pn + Fµ Pµ) tindep
2 statistic methods:
2. Nonlinear mixed model (MCMC - Bayesian)
[36Cl]meas = A (t + ΔF) PRCa + B (t + ΔF) PRK + C (t + ΔF) + Δ
PRCa = 42 ± 5 atoms
36
Cl (g Ca)-1 a-1
PRK = 142 ± 13 atoms
36
Cl (g K)-1 a-1
36
Cl spallation production rates (SLHL)
[Cltotal]
Ca:
Stone et al. 1996
48.8
2-7 ppm
66.8
Phillips et al. 2001
82
Swanson and Caffee 2001
this study
6-350 ppm
42-290 ppm
50
1-13 ppm
atoms 36Cl (g Ca)-1 a-1
K:
Evans et al. 1997
Phillips et al. 2001
162
137
6-350 ppm
217
Swanson and Caffee 2001
this study
0-315 ppm
142
42-290 ppm
1-13 ppm
atoms 36Cl (g K)-1 a-1
high Cltotal contents ➡ overestimation of spallation production rates???
Conclusions
calculations of 36Cl production due to low-energy capture very
uncertain ➡ avoid Cl-rich samples
spallation production rates - from simple linear model:
PRCa = 50 ± 4 atoms 36Cl (g Ca)-1 a-1
PRK = 142 ± 5 atoms 36Cl (g K)-1 a-1
spallation production rates - from non-linear mixed model:
PRCa = 42 ± 5 atoms 36Cl (g Ca)-1 a-1
PRK = 142 ± 13 atoms 36Cl (g K)-1 a-1
input 3 more sanidine (K) samples
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