Mass Fractionation and the Isotopic Anomalies of

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drite, and the abundance and isotopic composition of xenon and krypton are reported in the gases released by ... Many clues of early geologic events have been.
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E. WICKE U. A. OBERMANN, Z. Physik. Chem. N.F. (im Drude). — A. OBERMANN, Diplomarbeit, Münster 1970.

H e r r n P r o f . D r . E . WICKE möchten wir an dieser Stelle f ü r wertvolle H i n w e i s e und a n r e g e n d e Diskussionen herzlich d a n k e n . — D e r Deutschen Forschungsgemeinschaft d a n k e n w i r f ü r die Unterstützung unserer A r b e i t mit Personal- u n d Sachmitteln.

Mass Fractionation and the Isotopic Anomalies of Xenon and Krypton in Ordinary Chondrites E . W . HENNECKE a n d 0 . K . MANUEL Department of Chemistry, Universiy of Missouri, Rolla, Missouri (USA) (Z. Naturforsch. 26 a, 1980—1986 [1971] ; received 7 August 1971) The abundance and isotopic composition of all noble gases are reported in the Wellman chondrite, and the abundance and isotopic composition of xenon and krypton are reported in the gases released by stepwise heating of the Tell and Scurry chondrites. Major changes in the isotopic composition of Xe result from radiogenic Xe 129 and from variations in the isotopic mass fractionation pattern in the different temperature fractions. The isotopic composition of trapped krypton in the different temperature fractions of the Tell and Scurry chondrites displays smaller fractional changes than xenon, but the isotopic composition of these two gases covary in the manner expected from mass dependent fractionation. Many

clues

of

early

geologic

events h a v e

been

n o t e d that a c o m p a r i s o n o f t h e e a r t h ' s i n v e n t o r y o f

Kr

n o b l e g a s e s w i t h the s o l a r a b u n d a n c e s o f t h e s e ele-

and X e . T h e chemical inertness and volatile nature,

ments s h o w s preferential loss f r o m terrestrial mate-

e v e n at r e l a t i v e l y l o w t e m p e r a t u r e s , r e s u l t e d in al-

rial o f

most

w o r k o n n o b l e gases in terrestrial sediments

r e c o r d e d in t h e s t a b l e n o b l e g a s e s , H e , N e , A r ,

complete

condensable

loss

of

material

these

when

elements

solid

from

planetary

f o r m e d in o u r s o l a r s y s t e m . M a n y i s o t o p i c

more

the g a s e s l i g h t e r t h a n k r y p t o n .

Subsequent

h i g h c o n c e n t r a t i o n s o f x e n o n w h i c h , w h e n a d d e d to

anoma-

the a t m o s p h e r i c i n v e n t o r y o f n o b l e g a s e s , s h o w that

lies o f these e l e m e n t s h a v e b e e n g e n e r a t e d in s o l i d

the e a r t h ' s f r a c t i o n a t i o n

p l a n e t a r y m a t e r i a l s u b s e q u e n t t o this s e p a r a t i o n , b y

the h e a v i e s t

induced

g a s e s in s t o n e m e t e o r i t e s d i s p l a y a s i m i l a r

active

nuclear

decay

of

reactions more

and

by

abundant

natural

radio-

elements.

stable n o b l e

gases b y

nuclear

processes

of noble gases extends

stable gas, x e n o n .

nation pattern 4'

A l t h o u g h the g e n e r a t i o n o f i s o t o p i c a n o m a l i e s o f all t h e

5

SIGNER a n d

duction

by

n e o n and a r g o n in planetary material. T h e y

of

a covariance of A r 3 6 / A r 3 8 , N e 2 0 / N e 2 2 and

simple

isotopic

anomalies

masä

of

noble

fractionation

gases

at t h e t i m e

the s e p a r a t i o n o f t h e s e f r o m m o r e c o n d e n s a b l e m e n t s . I n 1 9 4 9 SUESS

1

a n d BROWN

2

ele-

ratios

independently

NUEL

Reprint requests to Prof. Dr. O. K. MANUEL, Department of Chemistry, University of Missouri-Rolla, Rolla/Missouri 65401, USA.

4

6

1

H . E. SUESS, J. Geol. 5 7 , 6 0 0

2

H. BROWN, The Atmosphere of the Earth and the Planets, University of Chicago Press, Chicago 1949.

[1949],

3

R . A . CANALAS, E . C . ALEXANDER, JR., a n d O . K . M A N U E L ,

5

7

in 7

generating

the r o l e o f

fractionation

isotopic

fractio-

atmospheric

and

re-

104 — 105.

SUESS 6 d i s c u s s e d

in

to

noble

w i t h the x e n o n p r e f e r e n t i a l l y

tained o v e r n e o n b y a f a c t o r

is

The trapped

well d o c u m e n t e d , there is also e v i d e n c e f o r the p r o of

found

3

matter

isotopic

meteoritic

mass

anomalies

Ne20/Ar36

gases.

r e p o r t e d v a r i a t i o n s in t h e t r a p p e d

of

noted MA-

Ne20/Ne22

J. H. REYNOLDS, Phys. Rev. Letters 4, 351 [1960]. O. K. MANUEL and M. W. ROWE, Geochim. Cosmochim. Acta 28. 1999 [1964]. P. SIGNER and H. E. SUESS. in: Earth Science and Meteorites, North-Holland Publ. Co., Amsterdam 1963. O. K. MANUEL, Geochim. Cosmochim. Acta 31, 2413 [1967].

J. Geophys. Res. 73, 3331 [1968].

Unauthenticated Download Date | 9/24/15 11:39 PM

and

Ne21/Ne22

ratios

in

the

different

temperature

d e r to o b t a i n a d d i t i o n a l d a t a w i t h w h i c h to e x a m i n e

f r a c t i o n s o f the F a y e t t e v i l l e m e t e o r i t e a n d s u g g e s t e d

the current

that t h e s e v a r i a t i o n s r e s u l t f r o m i s o t o p i c m a s s f r a c -

n o b l e g a s a n o m a l i e s in m e t e o r i t e s . S a m p l e s o f t h r e e

tionation.

o r d i n a r y c h o n d r i t e s w e r e u s e d f o r this i n v e s t i g a t i o n .

However,

PEPIN a n d

coworkers8-10

re-

framework

of

ideas

on

the

origin

of

p o r t e d t h a t t h e r e is n o s i g n t h a t d i f f u s i v e f r a c t i o n a t i o n is r e s p o n s i b l e f o r a n y o f t h e i s o t o p i c v a r i a t i o n s of

meteoritic

neon.

Recent

results

on

the

c o m p o s i t i o n o f t r a p p e d m e t e o r i t i c H e , N e a n d A r in the

laboratories

at

Minnesota,

Chicago

and

have been attributed to nuclear reactions other

authors15-17

served variations

have

maintained

result f r o m

Rice

~14, but

10

that

the

simple isotopic

obfrac-

tionation. F o r the h e a v y n o b l e gases, a s i m i l a r

divergence

o f o p i n i o n s h a s d e v e l o p e d . SRINIVASAN e t a l . 1 8 first suggested

that

spontaneous

fission

of

superheavy

elements m a y b e responsible f o r the enrichment heavy

xenon

isotopes

in

ANDERS a n d HEYMANN conclusion isotopes

by

carbonaceous

comparing

with

the e x c e s s

the c o n t e n t

carbonaceous

chondrites,

of

chondrites.

h a v e a r r i v e d at a s i m i l a r

19

of

volatile

and

heavy

xenon

elements

in

EBERHARDT e t al.

h a v e i n t e r p r e t e d the i s o t o p i c c o m p o s i t i o n

20

of

solar-

t y p e x e n o n as e v i d e n c e f o r l a r g e a m o u n t s o f

fissio-

genic xenon

in c a r b o n a c e o u s

KURODA a n d MANUEL

15

chondrites.

However,

recently pointed out

the e n r i c h m e n t o f h e a v y x e n o n i s o t o p e s in aceous and gas-rich meteorites enrichment of

heavy

neon

that

carbon-

is p a r a l l e l e d

isotopes. These

by

an

authors

c o n c l u d e d that the enrichment o f the h e a v i e r

isoto-

pes o f b o t h gases result f r o m i s o t o p i c mass f r a c t i o nation. Additional

evidence

f o r the p r o d u c t i o n

isotopic anomalies of meteoritic xenon and

of

krypton

b y fractionation have been reported f r o m noble gas analyses

of the

LEOVILLE

21

and

chon-

POTTER22

drites. T h i s s t u d y o f the i s o t o p i c c o m p o s i t i o n

Measurements

isotopic

of

noble

gases in ordinary chondrites was undertaken in

or-

8

R. 0 . PEPIN, Earth Planet. Sei. Letters 2 , 1 3

9

R. 0 . PEPIN, Origin and Distribution of the Elements, Pergamon Press, Oxford and New York 1968.

[1967].

10

D. C. BLACK and R. 0 . PEPIN, Earth Planet. Sei. Letters 6,

Relatively l a r g e meteorite s a m p l e s , w e i g h i n g a b o u t 10 g r a m s each, w e r e used in this study. T h e s e w e r e purchased f r o m the A m e r i c a n M e t e o r i t e L a b o r a t o r y ( A M L ) . T h e n a m e and type of each meteorite, the s a m p l e weight and the A M L c a t a l o g u e n u m b e r of the s p e c i m e n f r o m which o u r s a m p l e s were taken are as f o l l o w s : T h e W e l l m a n , T e x a s olivine bronzite chondrite, 1 0 . 8 8 8 g r a m s f r o m s p e c i m e n # H 1 2 . 5 6 ; the T e l l , T e x a s olivinie hypersthene chondrite, 8 . 4 7 4 g r a m s , f r o m s p e c i m e n # H 2 4 . 6 7 ; and the S c u r r y , T e x a s olivine bronzite chondrite, 7 . 9 0 9 g r a m s , f r o m s p e c i m e n # H 65.25. T h e s a m p l e s w e r e m o u n t e d in side-arm c h a m b e r s of a quartz extraction bottle. T h e s a m p l e s w e r e heated to ~ 6 0 ° C o v e r n i g h t to r e m o v e s u r f a c e c o n t a m i n a t i o n , the m o l y b d e n u m c r u c i b l e was d e g a s s e d at 1 8 0 0 ° C and the pressure of the system r e d u c e d to 5 x 1 0 - 8 T o r r . T h e extraction bottle and preliminary " g e t t e r s " w e r e then isolated f r o m the rest of the system b y metal b e l l o w s valves, the s a m p l e to b e analyzed w a s then d r o p p e d m a g n e t i c a l l y into the m o l y b d e n u m c r u c i b l e which was heated b y a r a d i o f r e q u e n c y i n d u c t i o n heater. A n o p t i c a l p y r o m e t e r was used to estimate the extraction temperatures. Each extraction temperature was m a i n tained f o r 3 0 minutes, and the evolved gases w e r e c l e a n e d in the extraction system b y titanium at 8 5 0 ° C and b y c o p p e r - o x i d e at 5 5 0 ° C . A f t e r these p r e l i m i n a r y " g e t t e r s " w e r e c o o l e d to r o o m temperature, the g a s e s w e r e then p u m p e d through the metal valve into a seco n d clean-up system b y adsorption on charcoal c o o l e d witl l i q u i d N 2 or solid C 0 2 . A f t e r isolating the g a s e s in the second c l e a n - u p system, they w e r e driven f r o m the charcoal at 2 0 0 ° C and e x p o s e d to a s e c o n d s u r f a c e of titanium s p o n g e at 8 5 0 ° C . In the case of parated into f o u r on c h a r c o a l ; the H e and N e , the 17

D . C . BLACK, M e t e o r i t i c s 4 , 2 6 0

[1969].

12

D. C. BLACK, Geochim. Cosmochim. Acta 34, 1 3 2

13

E . ANDERS, D . H E Y M A N N , a n d E . M A Z O R , G e o c h i m .

[1970].

E . M A Z O R , D . HEYMANN, a n d E . ANDERS, G e o c h i m .

B . SRINIVASAN, E . C . ALEXANDER, JR., O . K . M A N U E L , a n d

19

E . ANDERS a n d D . H E Y M A N N , S c i e n c e 1 6 4 , 8 2 1

20

P . EBERHARDT, J. GEISS, H . GRAF, N . GRÖGLER, U .

D. E. TROUTNER, Phys. Rev. 179,1166 [1969].

HENBÜHL,

Cosmo-

15

16

P. K . KURODA

and

0.

K . MANUEL,

21

Nature London

1113 [1970]. 0 . K. MANUEL, Meteoritics 5, 207 [1970].

H . SCHWALLER,

[1969].

J. SCHWARZMÜLLER,

KRÄ-

and

A.

STETTLER, Geochim. Cosmochim. Acta Supp. 1, 2, 1037 [1970].

Cosmo-

chim. Acta 34, 781 [1970].

Com-

18

chim. Acta 34,127 [1970]. 14

B . SRINIVASAN a n d O . K . M A N U E L , O n the I s o t o p i c

position of Trapped Helium and Neon in Carbonaceous Chondrites, Earth Planet. Sei. Letters, in press [1971].

395 [1969]. 11

W e l l m a n , the n o b l e gases w e r e sef r a c t i o n s f o r analysis b y adsorption b o i l i n g temperature of N 2 released sublimation temperature of C 0 2 re-

O . K . M A N U E L , R . J. W R I G H T , D . K . MILLER, a n d P .

K.

KURODA, J. Geophys. Res. 75, 5639 [1970].

227, 22

O. K .

M A N U E L , D . K . MILLER, R . J. W R I G H T , a n d P .

K.

KURODA, Solar Type Krypton, submitted to J. Geophys. Res. [1971].

Unauthenticated Download Date | 9/24/15 11:39 PM

leased A r , the f r e e z i n g p o i n t of H g released K r , and finally the X e w a s released f r o m the charcoal at 1 5 0 ° C . F o r T e l l and S c u r r y the n o b l e gases were p u m p e d into the s e c o n d c l e a n - u p system b y adsorption on charcoal c o o l e d with solid C 0 2 , and those gases not retained o n charcoal at this temperature ( H e , N e and A r ) were p u m p e d f r o m the s e c o n d clean-up system p r i o r to the final s c r u b b i n g on hot titanium ( 8 5 0 ° C ) . T h e k r y p t o n and x e n o n weTe let into the mass spectrometer as separate f r a c t i o n s b y selective adsorption of the x e n o n on charcoal at the freezing point of m e r c u r y . T h e g a s e s w e r e analyzed statically in a R e y n o l d s ' type 4 . 5 inch 6 0 ° sector mass spectrometer 2 3 . T h e mass s p e c t r o m e t e r w a s calibrated b e f o r e and after each s a m p l e b y analyzing small v o l u m e s of air ( ~ 0 . 0 1 c c S T P ) b y the same p r o c e d u r e of analysis as u s e d f o r the s a m p l e . T h e sensitivity of the spectrometer f o r each n o b l e g a s and the mass discrimination a c r o s s the isotopes of each gas w e r e c a l c u l a t e d b y c o m p a r i n g the p e a k heights with the a t m o s p h e r i c a b u n d a n c e s of n o b l e g a s e s 2 4 and the isotopic c o m p o s i t i o n of atmos p h e r i c n e o n 2 5 , a r g o n 2 6 , k r y p t o n 2 7 and x e n o n 2 8 . N o c o r r e c t i o n f o r mass discrimination was applied to helium. T h e errors reported in the isotope ratios are one standard deviation ( a ) f r o m the least squares line t h o r u g h the o b s e r v e d ratios as a f u n c t i o n of residence time in the mass spectrometer. Results f r o m b l a n k

analyses, w h e r e the identical p r o c e d u r e s w e r e f o l l o w e d f o r g a s e s evolved f r o m a hot m o l y b d e n u m c r u c i b l e , s h o w e d no significant c o n t a m i n a t i o n e x c e p t at m a s s 78. D u e to variations in the sensitivity of the mass spectrom e t e r the g a s c o n t e n t has much larger errors than the i s o t o p e ratios, such that the content of each n o b l e gas h a s an estimated e r r o r of + 2 0 % .

Results and Discussion 1. Noble Gases in Wellman T h e a b u n d a n c e s and i s o t o p i c c o m p o s i t i o n o f the n o b l e gases in W e l l m a n gether

with

the

noble

gases

in

are s h o w n in T a b l e

isotopic

composition

carbonaceous

of

chondrites

1 to-

trapped and

the

s o l a r - t y p e n o b l e g a s e s o b s e r v e d in g a s - r i c h m e t e o r i tes a n d

in the m o o n .

The isotopic composition

t r a p p e d H e , N e a n d A r in c a r b o n a c e o u s

of

chondrites

a r e t h e r a n g e o f v a l u e s r e p o r t e d in a c o m p r e h e n s i v e study

13'14

age values

and the t r a p p e d K r and X e are the aver29' 30

observed

in c a r b o n a c e o u s

tes. T h e i s o t o p i c c o m p o s i t i o n

chondri-

of solar-type He,

Ne

and A r are f r o m the Fayetteville gas-rich meteorite

7,

Table 1. Concentration and isotope composition of noble gases in the Wellman chondrite. Noble gases

Wellman observed

Trapped gas in carbonaceous chondrites

trapped

He 3 /He 4 He4

0.0253 ± 0 . 0 0 0 4 6.04 x 1 0 ~ 7 cc STP/gm

0.88x10- 4 5 . 2 5 x 1 0 - 7 cc STP/gm

Ne 20 /Ne 22 Ne 21 /Ne 22 Ne22

1.415 ± 0 . 0 0 3 0.876 ± 0 . 0 0 3 5.39 x 1 0 - 8 cc STP/gm

7.3 0.025 4.35x10-

Ar 38 /Ar 36 Ar 40 /Ar 36 Ar 36

0.450 ± 0 . 0 0 1 3143 ± 2 6 3.96 x I O " 9 cc STP/gm

0.23

Kr 80 /Kr 84 Kr 82 /Kr 84 Kr 83 /Kr 84 Kr 88 /Kr 84 Kr84

0.0423 ± 0 . 0 0 2 0.2048 ± 0 . 0 0 0 7 0.2045 ± 0 . 0 0 0 6 0.3058 ± 0 . 0 0 0 7 1.41 x l O - 1 0 cc STP/gm

Xe 1 2 4 /Xe 1 3 0 Xe 126 /Xe 130 Xe 128 /Xe 130 Xe 1 2 9 /Xe 1 3 0 Xe 131 /Xe 130 Xe 132 /Xe 130 Xe 134 /Xe 130 Xe 136 /Xe 130 Xe 130

0.0296 ± 0 . 0 0 0 2 0.0268 ± 0 . 0 0 0 2 0.508 ± 0 . 0 0 3 8.18 ±0.05 4.97 ±0.03 6.09 ±0.03 2.36 ±0.01 1.95 ±0.01 1 . 1 7 x 1 0 - " cc STP/gm

23 24 25

28

3.27x10