The case for a martian origin of the shergottites, II. Trapped and indigenous gas components in EETA 79001 glass

Earth and P1anetary 5c1ence Letter5, 77 (1986) 149-158

149

E15ev1er 5c1ence Pu6115her5 8.V., Am5terdam - Pr1nted 1n 7 h e Nether1and5 [6]

7he ca5e f0r a mart1an 0r191n 0f the 5her90tt1te5, 11.7rapped and 1nd19en0u5 9a5 c0mp0nent5 1n EE7A 79001 91a55 R.C. W1en5, R . H . 8 e c k e r a n d R . 0 . Pep1n Department 0f Phy51c5, Un1ver51ty0f M1nne50ta, M1nneap0115, MN 55455 (U.5.A.) Rece1ved May 1, 1985; rev15ed ver510n rece1ved Decem6er 4, 1985 Ana1y515 0f n1tr09en and 119ht n061e 9a5e5 1n a 1ar9e 5amp1e 0f 91a55 (11th0109y C) fr0m the antarct1c 5her90tt1te EE7A 79001 y1e1d5 a m1n1mum 615N > + 300%~ f0r the 150t0p1c c0mp051t10n 0f n1tr09en trapped 1n the 91a55. 7 h e new data fa11 0n the m1x1n9 11ne thr0u9h the mart1an atm05pher1c c0mp051t10n def1ned 6y ~15N v5. 4°Ar/14N f0r tw0 5ma11er 5amp1e5 ana1y2ed prev10u51y. 7 h e re5u1t5 fr0m a11 three 5amp1e5 are c0n515tent w1th a tw0-c0mp0nent n1tr09en 5y5tem 1n wh1ch - 84 pp6 0f trapped mart1an atm05pher1c N 15 m1xed 1n var1a61e pr0p0rt10n5 w1th an0ther, m0re therma11y 1a611e N c0mp0nent dur1n9 5tepped heat1n9. 7h15 5ec0nd c0mp0nent, wh1ch appear5 t0 6e 1nd19en0u5 t0 the 91a55 rather than ad50r6ed fr0m a1r and 15 pre5ent 1n am0unt5 that vary 6y m0re than a fact0r 0f 3 fr0m 5amp1e t0 5amp1e, may repre5ent v01at11e5 fr0m the mart1an 1nter10r. Data fr0m cry5ta111ne pha5e5 0f 5evera1 5NC mete0r1te5 1nd1cate that the 1nd19en0u5 9a5 may have 615N < -35%~ and 36Ar/14N ~ 3 X 10 -6, 51m11ar t0 the en5tat1te ch0ndr1te5. Ne0n c0mp051t10n5 1n E E 7 A 79001 91a55 5amp1e5 5u99e5t an earth-11ke va1ue 0f - 10.1 + 0.7 f0r the unkn0wn 2 ° N e / 2 2 N e rat10 1n the mart1an atm05phere. 7 h e n1tr09en-ar90n c0rre1at10n 5y5temat1c5 y1e1d trapped 4°Ar/36Ar = 2260 •+ 200, w1th1n err0r 0f the V1k1n9 va1ue. 7here 15 ev1dence that 36Ar/35Ar 1n the mart1an atm05phere 15 4.1 + 0.2, 5tr1k1n91y d1fferent fr0m terre5tr1a1 0r typ1ca1 ch0ndr1t1c rat105 near 5.3. Attr16ut10n 0f th15 10w va1ue t0 exce55 3~Ar 9enerated 0ver mart1an h15t0ry 6y 9a1act1c c05m1c-ray ( 6 C R ) 5pa11at10n 0f 5urface mater1a15 w0u1d 6e d1ff1cu1t f0r a num6er 0f rea50n5, am0n9 them the exce551ve 6 C R f1uence5 re4u1red and the a65ence 0f a c0rre5p0nd1n9 21Ne exce55.

1. 1ntr0duct10n 7he antarct1c 5her90tt1te E E 7 A 79001 wa5 recent1y 5h0wn t0 c0nta1n 150t0p1ca11y heavy n1tr09en 1n 1t5 91a55 pha5e [1]. 7h15 n1tr09en, wh1ch reached a max1mum mea5ured 615N va1ue 0f +200%0, c0u1d 6e exp1a1ned a5 trapped mart1an atm05pher1c N 2 m1xed w1th a 5ec0nd c0mp0nent made up 0f ad50r6ed terre5tr1a1 N 2, n1tr09en 1nd19en0u5 t0 the 5111cate5 0f the 5amp1e, 0r a c0m61nat10n 0f the tw0. 7 0 reduce the effect5 0f ad50rpt10n 0f terre5tr1a1 N 2 and there6y determ1ne the extent t0 wh1ch 1nd19en0u5 n1tr09en 15 1nv01ved 1n the m1xture 0f c0mp0nent5, we have re-ana1y2ed E E 7 A 79001 u51n9 an uncru5hed 91a55 5amp1e hav1n9 a much 5ma11er 5urface t0 v01ume rat10 than the ear11er 5amp1e5.

2. Exper1menta1 We 06ta1ned the new 5amp1e 0f E E 7 A 79001 91a55 1n the f0rm 0f a 51n91e, r0u9h1y 5pher1ca1 0012-821X/86/$03.50

• 1986 E15ev1er 5c1ence Pu6115her5 8.V.

p1ece. 7h15 5amp1e, 79001,22, came fr0m the 5ame 91a55 1nc1u510n a5 0ur prev10u5 79001,27 5amp1e5 [2]. 1n5pect10n 0f the 5amp1e w1th a 61n0cu1ar m1cr05c0pe revea1ed n0 1ar9e ve51c1e5 0r 06v10u5 fracture5. A 5ma11 p1ece wa5 rem0ved f0r preparat10n 0f a th1n-~ect10n. Petr09raph1c exam1nat10n 0f the 5ect10n 5hQwed n0 ev1dence f0r exten51ve crack5 0r 0ther penetrat10n5 1nt0 the 5amp1e that m19ht have acted a5 1nter10r trapp1n9 51te5 f0r n1tr09en 0f terre5tr1a1 0r191n. 7he 5amp1e wa5 wrapped 1n p1at1num f011 and 5t0red f0r tw0 m0nth5 under vacuum at r00m temperature 6ef0re ana1y515. Ana1y515 0f the 108.7 m9 5amp1e wa5 6y 5tepped heat1n9 1n the pre5ence 0f - 100 m70rr 0f 0xy9en, u51n9 the pr0cedure de5cr16ed 1n [1]. He11um, ne0n, and ar90n were determ1ned a10n9 w1th n1tr09en. 7he num6er 0f 5tep5 wa5 1ncrea5ed 0ver the prev10u5 ana1y5e5 t0 1mpr0ve the 5eparat10n 0f c0mp0nent5 1n the 91a55 and t0 pr0m0te the 10w-temperature rem0va1 0f terre5tr1a1 c0ntam1nant5 6ef0re the 1nd19en0u5 9a5e5 were re1ea5ed.

150

3. Re5u1t5 81ank-c0rrected he11um, ne0n, ar90n, and n1tr09en a6undance5 and 150t0p1c c0mp051t10n5 1n E E 7 A 79001,22 91a55, de519nated C ~ 3 , are 91ven 1n 7a61e5 1 and 2. 81ank ran9e5 were: 4 H e = 1.1 1 . 6 × 1 0 -9, 2 2 N e = 1 . 6 1 . 9 × 1 0 u , and-~6Ar = 6.8-7.9 × 10 12 c m 3 5 7 P ; 1 4 N = 2 1 0 - 4 4 0 p9. Data f0r tw0 ear11er 5amp1e5, C*e1 and C ~ 2 , are rep0rted 1n [1]. 1t 15 a p p a r e n t fr0m the data 1n 7a61e 2 that, de5p1te the pre5umed 10w 5urface area 0f C ~ 3 , there wa5 a pr061em w1th terre5tr1a1 c0ntam1nat10n 1n the 550 °, 700 °, and 900 ° 5tep5 f0r N 2 and, t0 a 1e55er extent, f0r ar90n. We prev10u51y ar9ued [1], 6a5ed 0n 81-5N va1ue5, that 11tt1e 0r n 0 n e 0f the h19h-815N n1tr09en trapped 1n C¢¢1 0r C ~ 2 wa5 re1ea5ed 6y 700°C, and we make the 5ame a55umpt10n f0r C:t¢:3. H0wever, 1t 15 c1ear fr0m the data f0r C:#:2 [1] that 5amp1e n1tr09en wa5 ev01ved at 900°C. 51m11ar1y, the C ~ 1 and C ~ 2 data 5h0w that trapped ar90n w1th h19h 4°Ar/3~Ar wa5 pre5ent 1n the 700°C 5tep, wh11e at 550°C the ar90n wa5 pred0m1nant1y terre5tr1a1. 8ecau5e the c0ntam1nat10n 0f C ~ 3 15 519n1f1cant1y 9reater 1n the 700°C 5tep f0r Ar and 900°C 5tep f0r 60th Ar and N than 1n the c0mpara61e 5tep5 f0r C a t 2 , we f 0 u n d 1t nece55ary t0 e5t1mate the am0unt5 0f the 5amp1e-der1ved 9a5e5 1n the5e c0ntam1nated 5tep5 u51n9 a t w 0 - c 0 m p 0 n e n t m1x1n9 ca1cu1at10n. A5 5een 1n 7a61e 2, repeat extract10n5 at the5e temperature5 9ave 150t0p1c re5u1t5 1nd1cat1ve 0f 5harp1y

10wer rat105 0f c0ntam1nant t0 trapped 9a5 than d1d the 1n1t1a1 extract10n5. 150t0p1c c0mp051t10n5 0f the unc0ntam1nated Ar and N c0mp0nent5 were theref0re a55umed t0 6e th05e mea5ured 1n the repeat 5tep5, except f0r 4°Ar/36Ar at 900°: here the h19h a n d 1mprec15e 4°Ar/36Ar va1ue 1n the 900R 5tep 5u99e5ted the m0re c0n5ervat1ve ch01ce 0f the avera9e 4°Ar/36Ar 1n the 900 ° and 900R fract10n5, w1th an appr0pr1ate1y 1ar9e uncerta1nty. 7 h e c0ntam1nant 150t0p1c c0mp051t10n wa5 a55umed f0r Ar t0 6e that mea5ured at 550°; f0r N, 1t wa5 taken a5 the avera9e ( + 10•+ 15%0) 0f the mea5ured 615N va1ue5 at 550 °, 700 °, 700R, a n d 1n a 61ank f0110w1n9 the 700 ° 5tep. 7he5e va1ue5 were taken rather than atm05pher1c c0mp051t10n5 t0 ref1ect the fact that re51dua15 0f the atm05phere, wh1ch may 6e fract10nated, are 1nv01ved. F0r n1tr09en, the n0natm05pher1c 615N a150 take5 1nt0 acc0unt the heav1er 150t0p1c rat10 expected 1n 0r9an1c c0ntam1nat10n. 7 h e u5e 0f atm05pher1c c0mp051t10n5 w0u1d make very 11tt1e d1fference 1n the re5u1t5. 7 h e a60ve a55umpt10n5 y1e1d the e5t1mate5 0f trapped Ar and N ta6u1ated 1n 7a61e 2 a5 700 C0rr and 900 C0rr. C0rrect10n5 0f th15 type c0u1d n0t have 6een d0ne 1n [1] 6ecau5e 0f the a65ence 0f repeat extract10n5 at the 5ame temperature5. 1n any ca5e, the 150t0p1c rat105 065erved 1n the var10u5 temperature 5tep5 0f C ~ 1 and Caa2 5u99e5t a re1at1ve1y 5harp tran51t10n fr0m c0ntam1nant-d0m1nated t0 5amp1e-d0m1nated 9a5e5, 50 5uch c0rrect10n5 w0u1d pr06a61y have 6een m1n0r. 7 h e am0unt5 0f trapped 9a5e5 der1ved a60ve

7A8LE 1 He11um and ne0n a6undance5 and 150t0p1cc0mp051t10n51n 91a555amp1e C:~3 (108.7 m9) fr0m EE7A 79001, 22, 121 7 3He 4He 22Ne 2°Ne/22Ne 21Ne/22Ne (°C) (10 ~°cm357P/9) (10-8cm3 57P/9) (10 1°cm3 57P/9) 550 700 700R a 900 900R ~ 1030 1100 1180 - 1500 1180R a

63.3 +1.6 9.89 •+0.27 2.08 _+0.11 2.43 •+0.10 0.135-+0.007 0.053 _+0.007 0.087 _+0.007 0.263 -+0.010 0.004_+0.005 0.030 _+0.006

70ta1

78.3 •+2.0

4.0•+4.0 3.9__+4.0 - 0 -+4 - 0 -+3 - 0 _+2 0.7 _+1.9 3.5 _+1.9 9.8 -+1.9 5.4+• 1.9 2.3 + 1.9

10.0 +4.0 4.40_+0.45 0.8 _+1.2 8.88+•0.91 1.90-+0.21 1.77 + 0.20 1.03 _+0.13 3.12 _+0.33 0.20+0.07 0.24 _+0.08

8.43__+0.19 5.09_+0.14 2.25_+0.43 2.59_+0.18 2.45+0.81 1.21 _+0.96 2.0 _+1.5 6.85 •+ 0.51 7.1 _+7.7 12.5 •+ 6.5

0.176-+0.005 0,437+•0.012 0.698_+0.061 0.650-+0.018 0.658-+0.030 0.663 + 0.032 0.670 _+0.048 0.268 _+0.009 0.54 -+0.19 0.060 _+0.016

29.5_+9.6

32.3 _+3.3

5.13+0.39

0.436_+0,016

a 5ec0nd extract10n5 at repeated temperature5

151 7A8LE 2 Ar90n and n1tr09en a6undance5 and 150t0p1c c0mp051t10n5 1n 91a55 5amp1e C ~ 3 (108.7 m9) fr0m EE7A 79001, 22, 121 7 (°C)

36Ar (10-10

550 700

40Ar (10-6

Cm 3 5 7 P / 9 )

137.7 +2.8 32.2 -+2.2

700C0rr a

7.3 +•

5.7

38Ar/ 36Ar

40Ar/ 36Ar

4.46•+0.09 1.91-+0.08

0.194•+0.002 0.195-+0.015

1.10•0.24

0.199•0.066

700R 6 900

2.91-+ 0.19 56.3 -+ 1.7

0.44-+0.02 7.14-+0.11

0.185-+0.015 0.227-+0.003

900 C0rr a

28

6.22 -+ 0.53

0 . 2 5 9 -+ 0.032

4- 14

900R 6 1030 1100 1180 -1500 1180R 6

1.50 -+ 28.88-+ 32.12-+ 68.9 -+ 13.41-+ 0.80 -+

70ta1 Ar 1> 700 70ta1 N >1900

184

0.19 0.64 0.73 1.5 0.43 0.30

0.48 -+0.02 5.61•0.10 7.24•0.11 13.38-+0.27 3.03•0.06 0.20 -+0.01

-+ 16

14N (pp6)

Cm 3 5 7 P / 9 )

37.7 -+0.8

324-+ 2 593-+ 35

674 •+28 280 -+18

=-1510-+460

0.273 -+0.013

2050 -+ 170

-

42.2-+ 2.8 170.0• 5.1

~ 2 2 2 0 4- 9 5 0

3170 • 380 1944-+ 27 2253-+ 40 1941-+ 46 2261-+ 57 2540 -+960

-1-+ 9 16-+ 4

-

1510-+ 84 1267-+ 33

0.305 • 0.021 0.245-+0.005 0.277•+0.008 0.295-+0.005 0.296-+0.009 0.248 +• 0.058

615 NA1R (%0)

24

30-+10 29•10

• 24

8.9 • 39.1-+ 31.9-+ 56.6• 26.5-+ 4.0 •

=- 144 • 2 8

2.0 2.0 2.0 2.4 4.3 1.8

144 • 28 171• 7 257-+14 309-+10 310-+17 232 -+ 98

191 • 25

242 • 16

a C0rrected f0r c0ntam1nat10n. 5ee text. 6 5ec0nd extract10n5 at repeated temperature5. a n d c 0 n t a m 1 n a n t c 0 m p 0 n e n t 5 15 a t 1ea5t a p p r 0 x 1 m a t e 1 y va11d. C 0 n 5 1 5 t e n t w1th th15, t h e re1ea5e t h r 0 u 9 h 9 0 0 ° 0f 5pa11at10n 38Ar, w h 1 c h 15 1n5en51t1ve t 0 t h e c 0 n t a m 1 n a t 1 0 n c 0 r r e c t 1 0 n , 15 - 15% f 0 r C # 3 c 0 m p a r e d t 0 - 17% f0r C # 2 . 7 h e re1at1ve1y 1ar9e e r r 0 r 5 f 0 r t0ta1 36Ar a n d 14N 1n 7 a 6 1 e 2,

c 0 r r e 5 p 0 n d t 0 re1ea5e5 0 f 22 +• 8% a n d 17 •+ 13% 0 f t h e t0ta1 t r a p p e d 36Ar a n d 14N 1n C # 3 at t e m p e r a t u r e 5 < 900 °, 51m11ar e n 0 u 9 h t 0 t h e c 0 r r e 5 p 0 n d 1n9 fract10na1 re1ea5e5 ( - 16% a n d - 17%) f r 0 m C#2, h e a t e d at t h e 5 a m e t e m p e r a t u r e 5 t h r 0 u 9 h 9 0 0 °, t 0 5u99e5t t h a t th15 d e c 0 n v 0 1 u t 1 0 n 0 f t r a p p e d

~15000

1 ,

~

300

300

(a)

(6)

....

c~3

0

4 J 11000 EE7A

79001

1

11 ~1500°

6LA55 200

200

1030 ~

C#2

1

0 10600

900°R

0

100

100 108.7

m9 5amp1e

;

11700

,•

/1 ,

)

_

0

(C #3)

c~1

7000R ,000

0

pp6

550°

N

~

1

0

ppm

~

] 100

1

•

200

1 2

N" 1 ~

pp6

0

N

[ ~oo

----4..-

1 200

1 300

1 400

500

F19. 1. N1tr09en 150t0p1c c0mp051t10n5 v5. am0unt5 re1ea5ed 1n 5tepped heat1n9 (a) fr0m 5amp1e C # 3 and (6) fr0m a11 three EE7A 79001 91a55 5amp1e5. 7he 5ma11 N re1ea5e 1n the 1180R fract10n fr0m C # 3 (7a61e 2) 15 n0t 5h0wn.

152 c0mpared t0 the prev10u5 5amp1e5 [1], ar15e ma1n1y fr0m uncerta1nt1e5 1n the der1vat10n 0f the5e 10wtemperature a6undance5. Mea5ured 615N va1ue5 v5. n1tr09en re1ea5e are 5h0wn f0r C ~ 3 1n F19. 1a, where the 10w-temperature 5tep5 d0m1nated 6y c0m6u5t10n 0f 0r9an1c c0ntam1nant5 and re1ea5e 0f ad50r6ed 9a5e5 are p10tted t0 the 1eft 0f [ N ] = 0 . Re1ea5e5 0f 5uch am0unt5 0f c0ntam1nant n1tr09en at 10w temperature5 are n0t unu5ua1, th0u9h they 5tand 1n c0ntra5t t0 the c1ean11ne55 0f the n061e 9a5e5. 7he max1mum 815N va1ue 0f +310%~ 1n C2f3 15 100%c, a60ve the prev10u5 max1mum f0r 79001 91a55 1n C ~ 2 . 5pa11at10n c0rrect10n5 are 5ma11, am0unt1n9 t0 14 •+ 5%~ 1n the c0m61ned 1180 ° and 1500 ° fract10n5 fr0m C:~3 1f a11 the 5pa1109en1c ~5N 15 re1ea5ed at the5e temperature5, and 6 + 2%c 1n the 6u1k 615N va1ue (7a61e 2). N1tr09en a6undance5 and 150t0p1c c0mp051t10n5 f0r a11 three 91a55 5amp1e5 are d1rect1y c0mpared 1n F19. 16. 70 the r19ht 0f [N]= 0, 6~5N 1ncrea5e5 w1th 1ncrea51n9 temperature 1n a11 three 5amp1e5, d1a9n05t1c 0f m1x1n9 0f h19h-6~5N trapped N re1ea5ed preferent1a11y at h19h temperature w1th a 1e55 t19ht1y 60und 10w-615N c0mp0nent. 7he 1nver5e re1at10n 6etween avera9e 6~5N and n1tr09en c0ntent 1n F19. 16 dem0n5trate5 that the 6u1k m1x1n9 rat10 0f the tw0 c0mp0nent5 15 var1a61e, w1th 10w-6~5N n1tr09en m05t a6undant 1n C:~1 and 1ea5t 1n C ~ 3. 4. D15eu5510n

4.1. 7w0-c0mp0nent N-Ar m1x1n9 Ana1y5e5 0f the C ~ 1 and C¢¢2 5amp1e5 [1] p01nted 5tr0n91y t0 the pre5ence 0f trapped mart1an atm05phere 1n EE7A 79001 91a55 f0r tw0 rea50n5: n0n-5pa1109en1c n1tr09en 1n C ~ 2 wa5 150t0p1ca11y heav1er (615Nm~× --- + 200%~) than 1n any kn0wn mete0r1t1c, 501ar, 0r p1anetary re5erv01r 0ther than the c0ntemp0rary mart1an atm05phere (6J5N = 620 •+ 160%~ [3]); and the m1x1n9 11ne def1ned 6y the C ~ 1 and C:~2 data p01nt5 0n a p10t 0f 615N v5. 4°Ar/14N pa55ed we11 w1th1n err0r thr0u9h the mart1an atm05pher1c c0mp051t10n. 7he recent rep0rt [4] 0f 6~5N va1ue5 9reater than +900%c 1n the 8encu661n mete0r1te 1nva11date5 the f1r5t 0f the5e ar9ument5, 6ut d0e5 n0t a1ter the 5ec0nd.

7he C:~3 data re1nf0rce the ear11er ca5e f0r mart1an atm05pher1c n1tr09en 1n the 91a55. 7he m05t pr0m1nent new re5u1t, 5een 1n F19. 1, 15 the apprec1a61e 1ncrea5e, t0 -300%0, 0f the 10wer 11m1t f0r 8~5N 1n the 150t0p1ca11y heavy trapped n1tr09en c0mp0nent. Add1t10na11y, an updated ver510n 0f the tw0-c0mp0nent m1x1n9 re1at10n (F19. 2a, where 5pa11at10n-c0rrected 6u1k 61-5N 15 p10tted v5. 4°Ar/14N ( a t 0 m / a t 0 m ) f0r Ar,and N re1ea5ed fr0m a11 three 5amp1e5 at 7>~ 700 ° and 7>~ 900 ° re5pect1ve1y) 5h0w5 that the C ~ 3 data p01nt 15 c0n515tent w1th the 0r191na1 C ~ 1 - C # 2 m1x1n9 11ne. H0wever, 6ecau5e 0f 1t5 re1at1ve1y 1ar9e err0r5, the new p01nt d0e5 n0t add1t10na11y c0n5tra1n the uncerta1nty 1n the 11ne. 51nce the max1mum 615N va1ue 5een 1n 0ur ana1y5e5 15 0n1y a60ut +300%c, 0ne 5h0u1d n0t 0ver100k the p05516111ty that the pure trapped n1tr09en c0mp0nent 15 character12ed 6y 50me va1ue 10wer than the pre5ent-day mart1an 61-5N 0f 620 +• 160% [3]. H0wever, the a65ence 0f a p1ateau 1n 615N ar9ue5 f0r var1a61e m1x1n9 0f a tw0-c0mp0nent 5y5tem at a11 temperature5 a60ve 900 ° , and 1mp11e5 a 615N 9reater than 300% f0r the heavy c0mp0nent. 1t 15 11ke1y that the tw0 c0mp0nent5 are n0t c0mp1ete1y 5epara61e 6y 5tepped heat1n9 at any temperature. F0r ar90n, we n0te that 1n a11 the 11th0109y C 5amp1e5 mea5ured 50 far, e5pec1a11y 1n that 0f 5w1nd1e et a1. [5], the 4°Ar/36Ar rat105 vary c0n51dera61y 6etween h19h-temperature 5tep5.7h15 may 6e due t0 d1fferent1a1 me1t1n9 0f m1nera1 pha5e5 h01d1n9 m0re 0r 1e55 0f the 10w-4°Ar/36Ar 9a5 c0mp0nent. 1n n1tr09en, h0wever, th15 var1at10n 15 n0t 065erved; the 615N va1ue5 rema1n r0u9h1y e4ua1 fr0m 1160 ° t0 1500 ° 1n 60th C # 1 and C ~ 3 .

4.2. Mart1an atm05pher1c 4°Ar/ ~Ar rat10 A p10t ana1090u5 t0 F19. 2a, w1th 36Ar rep1ac1n9 4°Ar, 15 5h0wn 1n F19. 26. 7he three p01nt5 are a9a1n c011near and 1nterpreta61e a5 a m1x1n9 re1at10n5h1p pa551n9 w1th1n err0r thr0u9h the mart1an atm05pher1c c0mp051t10n. 7he tw0 m1x1n9 11ne5 1n F19. 2 may 6e u5ed t0 der1ve 40Ar/14N and 36Ar/14N rat105, and theref0re a 4°Ar/36Ar rat10, f0r any va1Ue 0f 815N. F0r examp1e, f0r a c0mp0nent character12ed 6y 615N 1n the mart1an atm05pher1c ran9e 0f 620•+ 160%0, the c0rre5p0nd1n9 4°Ar/36Ar rat10 91ven 6y the c0rre1at10n5 15 2260 •+

153

800

6

15

• NA1R 1%0)

800~

(a)

v00~

700

60(

600~

50C

500~

40£

400F

300

300~ MAR5 (~A7M05PHERE (~EAR7H A7M05PHERE

200

100F 0~

0

-100

1 0

-40~0 1

01.1

~ 40Ar/14N)A70M

0.01 •

0•2

•

01.3

(6)

200t

100

~

615NA1R ( % 0 )

•

-1001

•

/ 1 0

MAP5 A7M05PHERE EAR7H A7M05PHERE

C•1

(36Ar/14N)A70M X10 -5 ~

110

,5

F19. 2. M1x1n9 11ne5def1ned 6y 1nte9rated 615N v5. (a) 4°Ar/14N and (6) 36Ar/14N f0r EE7A 79001 91a55e5C#1, C#2, and C#3. 80th 615N and 36Arare c0rrected f0r 5pa11at10n, a55um1n9 an exp05ure a9e 0f 0.6 •+ 0.2 My. Mar5 atm05phere data were fr0m [3,7]. We ad0pt an uncerta1nty 0f • 750 1n the 4°Ar/36Ar rat10 0f 3000 91ven w1th0ut err0r 1n [7], t0 enc0mpa55 the ran9e 1n the 0r191na1va1ue 0f 2750 •+ 500 [6]. 7he err0r enve10pe 1n (6) 15 that 91ven d1rect1yfr0m the 1ea5t-54uare5a190r1thm 0f Y0rk [14]. 7he data p01nt5 1n (a) are 50 near1y c011near that the Y0rk err0r 15 m1nute. We theref0re der1ved a m0re c0n5ervat1ve e5t1mate 0f the uncerta1nty 1n the 11ne1n (a) 6y d15p1ac1n9the C#3 data p01nt t0 the 11m1t50f 1t5 h0r120nta1 10 err0r 6ar and reca1cu1at1n9 the Y0rk f1t5 at each 11m1t.7he f1t5 y1e1ded 6y the5e reca1cu1at10n5 def1ne the 1nner (dark 5haded) err0r enve10pe, the err0r5 1n the5e f1t5 the extreme (119ht 5haded) uncerta1nt1e5.

200. 7h15 15 51m11ar t0 the m05t prec15e1y mea5ured max1mum 4°Ar/36Ar rat105 1n 5tepped heat1n9 0f a11 three 91a55 5amp1e5 a n d t0 the t r a p p e d 4°Ar/36Ar rat10 der1ved 6 y 0ther mean5 [1, ta61e 5]. A55umpt10n 0f e n d - m e m 6 e r 815N va1ue5 1e55 t h a n 620%0, 6ut 1ar9er t h a n the mea5ured max1m u m 0f - 300%0, 1ead5 t0 4°Ar/36Ar rat105 5119ht1y 1e55 than 2260 ( - 2 2 0 0 at 815N = 300%0). 7h15 am619u1ty 1n the e n d - m e m 6 e r c0mp051t10n ex15t5 6ecau5e 0ur d a t a can 0n1y c0n5tra1n the t r a p p e d c 0 m p 0 n e n t t0 11e at 0r a60ve - 300%0 0n the 11ne5 1n F19. 2 . 7 h e va1ue 0f 2260 + 200 11e5 near the 10w e n d 0f the ran9e apparent1y a110wed 6y the V1k1n9 data (4°Ar/36Ar 0r191na11y 2 7 5 0 + 500 [6], 1ater r e p 0 r t e d a5 3000 w1th0ut err0r [7]), 6ut 15 c0n515tent w1th the5e data, a n d m a y pr0v1de the 6e5t e5t1mate f0r the mart1an atm05pher1c rat10 6ecau5e 0f the 5ma11er err0r a550c1ated w1th 0ur der1vat10n.

4.3. 7he [0W-~15Nc0mp0nent M1x1n9 0f 150t0p1ca11y 119ht n1tr09en w1th the h e a v y n1tr09en t r a p p e d 1n the 91a55 15 d e m 0 n 5trated 6y the 5tepped 815N pattern5 1n F19. 1 . 7 h e 4ue5t10n 15 whether the 119ht c 0 m p 0 n e n t 15 terre5tr1a1 0r 1nd19en0u5 t0 the mete0r1te. 8ecau5e 0f the 1ar9e a m 0 u n t 0f terre5tr1a1 c0ntam1nat10n 065erved 1n C # 3 up t0 900 °, 1t 15 06v10u5 that 0ur 0r191na1 06ject1ve 1n ana1y21n9 th15 51n91e 91a55 f r a 9 m e n t ha5 6een c0mpr0m15ed: we c a n n 0 t exc1ude a terre5tr1a1 c0ntr16ut10n t0 the 10w-815N c 0 m p 0 n e n t 1n h19h-temperature 5tep5 51mp1y 0n the 6a515 0f 5urface area ar9ument5, 91ven the re1at1ve am0unt5 0f 10w-temperature c0ntam1nant5 1n C # 3 a n d 1n 0ur 0ther tw0 91a55 5amp1e5 [1]. H0wever, there 15 1nf0rmat10n 1n F19. 2 that re1ate5 d1rect1y t0 the 0r191n 0f th15 c 0 m p 0 n e n t . N 0 t e that

154

the terre5tr1a1 atm05phere 11e5 0n 0pp051te 51de5 0f the m1x1n9 11ne5 1n the tw0 p10t5. 7h15 cann0t re5u1t 51mp1y fr0m ad50rpt10n 0f a1r, w1th an a550c1ated e1ementa1 fract10nat10n 0f Ar and N; an unrea50na61y 1ar9e 150t0p1c fract10nat10n 0f Ar w0u1d a150 6e re4u1red. F0r an end-mem6er w1th an a55umed 815N 0f 0%0, the c0rre1at10n5 y1e1d a 4°Ar/3~Ar rat10 0f - 1 8 0 0 + 700, far fr0m the terre5tr1a1 va1ue 0f 296. 7heref0re ar90n 1n the 10w-815N c0mp0nent 0f the 91a55 15 pr1mar11y 1nd19en0u5, and 6y 1mp11cat10n the n1tr09en 15 a5 we11.1f n1tr09en were unre1ated t0 the ar90n 1n th15 c0mp0nent, c011near1ty 0f the data p01nt5 1n F19. 2 w0u1d n0t 6e expected. We c0nc1ude fr0m th15 065ervat10n that the 150t0p1ca11y 119ht n1tr09en 15 n0t ad50r6ed terre5tr1a1 N2, 6ut 15 1ar9e1y 1nherent 1n the 5amp1e and var1a61e 1n am0unt. 7he 50urce 0f the unexpected1y 1ar9e am0unt5 0f terre5tr1a1 9a5e5 re1ea5ed fr0m Ce~3 at 10w temperature5 15 unkn0wn. 1t 15 p055161e that they were trapped 1n 5ec0ndary a1um1n05111cate m1nera15 5uch a5 th05e 065erved 0n 91a55y 51te5 1n 11th0109y A and tentat1ve1y attr16uted t0 terre5tr1a1 weather1n9 [8]. 1f 50, the5e weather1n9 pr0duct5 mu5t c0mp1ete1y dec0mp05e 0r de9a5 at temperature5 < 900°C. 7he 10w-6a5N c0mp0nent 15 0f 1ntere5t 1n that 1t c0u1d repre5ent 9a5e5 a550c1ated w1th a 6a5a1t1c 50urce re910n 1n the mart1an mant1e. 7he 91a55 5amp1e5 are n0t very u5efu1 1n d1rect1y revea11n9 1t5 e1ementa1 and 150t0p1c character15t1c5, 6ecau5e 0f the terre5tr1a1 c0ntam1nat10n at the 10w temperature5 where the F19. 1 pr0f11e5 5u99e5t 1t w0u1d 6e ev01ved 1n pure5t f0rm. 8ut the ev1dence f0r a tw0-c0mp0nent 5y5tem w0u1d 5eem t0 re5tr1ct the c0mp051t10n t0 50me p051t10n 0n the F19. 2 m1x1n9 11ne5 6e10w the C # 1 p01nt. M0re0ver, 1f th15 c0mp0nent wa5 pre5ent 1n the 5111cate5 fr0m wh1ch the 91a55 f0rmed, n0n-5pa1109en1c 9a5e5 1n the 6a5a1t (11th0109y A) 5urr0und1n9 the 91a55 pha5e51n EE7A 79001, and 1n the 0ther, 1ar9e1y 91a55-free 5NC mete0r1te5, 5h0u1d pr0v1de mea5ure5 0f the 5ame 0r c105e1y re1ated 1nd19en0u5 c0mp051t10n5. 1n F19. 3 we have rep10tted the F19. 26 m1x1n9 11ne 0n a 109ar1thm1c 36Ar/14N 5ca1e, add1n9 data fr0m 0ther 501ar 5y5tem N-Ar re5erv01r5 f0r c0mpar150n. 1t 15 c1ear that 501ar-11ke and C1-CM ch0ndr1te 9a5e5 are d15t1nct1y d1fferent fr0m c0mp051t10n5 w1th1n the 5haded exten510n 0f the m1x1n9 11ne 6e10w C:~1. 7he 11ne d0e5 1nter5ect the

800

L

1

-615

1

1

1

1

1

NA1R (%0)

•MAR5

A7M05PHERE

600

400

~] C ~ 3 200 0

Rena220

C#2

L

50LAR

W1N[

Ce C1,CM N r~-~ / ~ ; C / f

r---, ~,~ LUNAR 501L5

EAR7H A7M0--

0,CV

•ECh

(36Ar/14N)at0m

200 10 -7

10 5

10 3

10 1

F19. 3. EE7A 79001 91a55data and m1x1n911nefr0m F19. 26 0n a 109ar1thm1c36Ar/14N 5ca1e. 50urce5 0f c0mpar150n data f0r 0ther 501ar 5y5tem N-Ar re5erv01r5 a5 f0110w5:car60nace0u5 ch0ndr1te5 (c1, cM, Rena220, c0, cv), Ar fr0m [22], N fr0m [23]; en5tat1te ch0ndr1te5 (ECh), Ar fr0m [24], N fr0m [23]; 5Nc mete0r1te5 (5,N,c), Ar (c0rrected f0r 5pa11at10n) fr0m [25], N fr0m [11]; EE7A 79001 11th0109yA (E), Ar and N fr0m [1]; 501ar w1nd, 36Ar/14N (-2.8×10 -3) fr0m [26], 815N (-150%0) fr0m [27]; 1unar 50115,Ar fr0m [26,28 31], N fr0m [26,28,32,331. data f1e1d5 f0r C 0 - C V ch0ndr1te5 and en5tat1te ch0ndr1te5, 50 a5 far a5 N-Ar c0mp051t10n5 are c0ncerned the 1nd19en0u5 c0mp0nent 1n 79001 c0u1d re5em61e 9a5e5 1n e1ther 0f the5e mete0r1te c1a55e5.8ut ne1ther CV-11ke mater1a1--pr0p05ed a5 a p055161e v01at11e 50urce f0r 60th Mar5 and Earth [9]--n0r en5tat1te ch0ndr1te5 can acc0unt 1n a 5tra19htf0rward way f0r 0ther character15t1c5 0f the mart1an atm05phere, n0ta61y the h19h K r / X e rat10 and the 5u99e5t10n that n0nrad109en1c trapped Xe 1n the EE7A 79001 91a55e5 re5em61e5 terre5tr1a1 Xe m0re c105e1y than AVCC Xe [1,5,10]. 7he few ex15t1n9 data 0n N-Ar 5y5temat1c5 1n n0n-91a55y 5NC 5amp1e5 are p10tted a5 the 5 (5her90tty), N (Nakh1a), C (Cha5519ny) and E ( E E 7 A 79001A) 60xe5 1n F19. 3. 7he mea5ured ran9e 0f 36Ar/14N va1ue5 appear5 t0 6e 51m11ar t0

155

that 1n en5tat1te ch0ndr1te5. 8u1k 615N va1ue5 11e a60ve the m1x1n9 11ne 0ver th15 ran9e, 6ut the pr0n0unced 615N var1a6111ty 1n 5tepped heat1n9 0f the5e 5amp1e5 [1,11] may ref1ect the pre5ence 0f terre5tr1a1 n1tr09en c0ntam1nat10n, w1th 6a5N >• 0%0, wh1ch w0u1d pertur6 the mea5urement5 t0ward h19her 815N and 10wer 36Ar/14N. 7he m1n1mum 8~5N va1ue5 0f ar0und -35%0 rep0rted f0r 5her90tty and Cha5519ny [11] are c0mpat161e w1th an unpertur6ed c0mp051t10n 0n 0r near the F19. 3 m1x1n9 11ne, 1f the1r actua1 36Ar/14N rat105 are < 3 × 1 0 6. 4.4. 51t1n9 0f the tw0 c0mp0nent5

ve51c1e-f0rm1n9 9a5e5 are 5t111 pre5ent 1n the 6u661e5, a n0n-therma1 exper1ment (e.9., cru5h1n9) m19ht re1ea5e them preferent1a11y, w1th0ut d1ffu51ve m1x1n9 w1th 0ther c0mp0nent5. 7here rema1n5 the pr061em 0f the h19h1y n0nun1f0rm d15tr16ut10n 0f the 1nd19en0u5 9a5e5. 1t may 6e that var1at10n5 1n 5h0ck-me1t temperature5, c0011n9 rate5, and e5cape pathway5 re5u1ted 1n vary1n9 de9ree5 0f 0ut9a551n9 eff1c1ency, even fr0m d1fferent part5 0f a 51n91e 91a55 1nc1u510n. A very 5cattered d15tr16ut10n 0f 1nd19en0u5 9a5 carr1er5 1n the 0r191na1 6a5a1t1c mater1a1 c0u1d a150 have 6een a c0ntr16ut1n9 fact0r 1n the 065erved heter09ene1ty. 4.5. 7rapped ne0n

61ven va1ue5 0f 615N > 300%0 1n the heavy N c0mp0nent, a6undance5 0f th15 c0mp0nent der1ved f0r the three 91a55 5amp1e5 are 5tr1k1n91y un1f0rm. F0r the 5pec1f1c va1ue5 615Ntrapped= +620%0 and 615N1nd19..... = - 3 5 % 0 (re5u1t5 are n0t very 5en51t1ve t0 the 1atter va1ue), the a6undance 1n a11 three 5amp1e5 15 84 pp6 N w1th1n 5%. 0 t h e r ch01ce5 0f 815Ntrapped y1e1d d1fferent a6501ute am0unt5 0f the trapped c0mp0nent, 6ut 51m11ar 5amp1e-t0-5amp1e c0n515tency. 1n c0ntra5t, d15tr16ut10n 0f the 119ht c0mp0nent 15 h19h1y var1a61e: am0unt5 1n C ~ 1 exceed th05e 1n C ~ 3 6y m0re than a fact0r 0f three. 7h15 065ervat10n, t09ether w1th the exper1menta1 ev1dence that the tw0 c0mp0nent5 0ut9a5 d1fferent1a11y and are theref0re n0t un1f0rm1y m1xed 1n 51tu, p05e5 50me 1ntere5t1n9 4ue5t10n5 a60ut 9a5 1nject10n/retent10n pr0ce55e5 and the phy51ca1 nature5 0f the h05t 51te5. 7he pre5ence 0f 5ma11 ( - 10-50/~m) ve51c1e5 1n the 11th0109y C 91a55 [8] 1mmed1ate1y 5u99e5t5 0ne p05516111ty: that the h19h-815N c0mp0nent wa5 1nc0rp0rated 1nt0 the m01ten 5111cate51n m1cr06u661e5, w1th a h19h en0u9h p0pu1at10n den51ty ( > 104/9) t0 acc0unt f0r the 065erved un1f0rm1ty 0f trapped 9a5 c0ntent5 1n 5amp1e ma55e5 ran91n9 fr0m - 10 t0 100 m9. F0rmat10n and free21n9-1n 0f 6u661e5 a5 a c0n5e4uence 0f 5h0ck-1mpe11ed 9a5 1nject10n 1nt0 a tran51ent 5111cateme1t w0u1d n0t 6e unexpected. 7he 119ht N c0mp0nent, 6y hyp0the515 pre5ent 1n the 5111cate5 pr10r t0 5h0ck, m19ht then 6e d15501ved 1n the 91a55 0r he1d 1n 1nd19en0u5 5ec0ndary m1nera15 w1th1n the 91a55 [8], 1n 51te5 0f 10wer act1vat10n ener9y f0r therma1 re1ea5e. 1f the

EE7A 79001 91a55 c0nta1n5 11tt1e trapped Ne [1,12], and mea5urement5 are c0mp11cated 6y 10w-temperature c0ntam1nat10n and 4°Ar2+ and C0~ + 1nterference5. Ana1y5e5 0f C # 2 and C # 1 y1e1ded (2°Ne/36Ar)trapp~d 0f 0.16 and < 1.1 re5pect1ve1y [1], wh1ch 5pan the uncerta1nty ran9e ( - 0.15-1.0) f0r th15 rat10 1n the V1k1n9 mea5urement [13]. 1n C # 3 , exc1ud1n9 the c0ntam1nated 550 ° fract10n, (20Ne/36Ar)trapped 15 0.40•+ 0.16, 1nd15t1n9u15ha61e fr0m the m05t pr06a61e mart1an atm05pher1c va1ue 0f 0.43. 7he 2°Ne/22Ne rat10 1n the mart1an atm05phere wa5 n0t determ1ned 6y V1k1n9, and c0u1d n0t 6e der1ved w1th c0nf1dence fr0m prev10u5 5tepped heat1n9 exper1ment5 [1,12]. H0wever, 1n C # 3 , there wa5 a re1at1ve1y 1ar9e re1ea5e 0f n0n5pa1109en1c 22Ne at 1180 ° (7a61e 1); max1mum ev01ut10n 0f trapped Ar and N a150 0ccurred at th15 temperature. A 1ea5t-54uare5 c0rre1at10n [14] 0f 2°Ne/22Ne v5. 2/Ne/22Ne f0r ne0n re1ea5ed at 7>~ 700R, heav11y we19hted 6y the 1180 ° datum, y1e1d5 (20Ne/22Ne)trapped = 9.6 •+ 0.6, a55um1n9 a 21Ne/22Ne rat10 0f - 0.03 + 0.01 typ1ca1 0f 5pa11at10n-free 501ar 5y5tem ne0n c0mp0nent5. A m0re c0nv1nc1n9 three-150t0pe ne0n c0rre1at10n rep0rted 6y [5] y1e1d5 2 ° N e / 2 2 N e = 10.6 •+ 0.6 at 21Ne/22Ne = 0.03, w1th1n err0r 0f 0ur e5t1mate. 7he avera9e va1ue 0f 10.1 + 0 . 7 fr0m the tw0 ana1y5e5 15 c105e t0 the terre5tr1a1 rat10 0f 9.8 and, 1f va11d f0r the mart1an atm05phere, empha512e5 the earth-11ke nature 0f m05t 0f the n0n-rad109en1c mart1an n061e 9a5e5 [1].

156

4.6. 5pa11at10n 9a5e5 and trapped-~Ar/3~Ar Pr0duct10n 6y 9a1act1c c05m1c ray5 acc0unt5 f0r a11 the 3He and > 95% 0f the 21Ne 1n the 91a55. A11 three 5amp1e5 have 1dent1ca1 3He5p C0ntent5. 7he 21Ne5p C0ntent 0f C:~3 15 13.6 •+ 1.5 X 10 -1° cm 3 5 7 P / 9 , wh1Ch 15 --20% h19her than C:~1 and C ~ 2 a6undance5 [1] and C105e t0 the avera9e (14.3 •+ 2.6 × 10 -1° cm 3 5 7 P / 9 ) f0r a11 79001 5amp1e5 1n [12]. Err0r5 1n the f0ur 5et5 0f mea5urement5 0ver1ap, and the EE7A 79001 exp05ure a9e 0f --0.6 •+ 0.2 m.y. deduced 1n [1] 15 e55ent1a11y unaffected. 1n c0ntra5t t0 3He~p and 21Ne~v, 5pa1109en1c 35Ar 15 a m1n0r fract10n 0f the t0ta1 35Ar a6undance. A55um1n9 36Ar/38Ar 1n the trapped c0mp0nent 15 5.35 •+ 0.10, a5 1n the terre5tr1a1 atm05phere and m05t 0ther n0n-5pa1109en1c 501ar 5y5tem Ar re5erv01r5, 35Ar5p 1n C¢¢3 15 ca1cu1ated t0 6e 17.9 + 3.2 X 10 10 cm 3 5 7 P / 9 . 7h15 15 w1th1n err0r 0f the C # 1 and C # 2 a6undance5 der1ved w1th the 5ame a55umpt10n [1], 6ut 15 m0re than f0ur t1me5 the avera9e 38Ar5p C0ntent 0f 4.4 •+ 0.8 × 10 10 Cm3 5 7 P / 9 06ta1ned fr0m 51X 5amp1e5 0f EE7A 79001 11th0109y A [1,12]. 7h15 avera9e 11th0109y A a6undance y1e1d5 the 5ame c05m1c-ray exp05ure a9e a5 d0 5pa1109en1c 3He and 21Ne 1n 60th 11th01091e5 [1,12]; there 15 thu5 n0 ev1dence f0r 9a5 1055 fr0m e1ther mater1a1. 51nce tar9et e1ement c0ncentrat10n5 are 51m11ar 1n the tw0 11th01091e5 [1], and 0ne theref0re expect5 51m11ar 38Ar5p a6undance5, the data 1mp1y that (36Ar/35Ar)trapped 15 aCtUa11y mUCh 10Wer than 5.35. A55Um1n9 that the avera9e 3~Ar~p 1n 11th0109y A app11e5 t0 the 91a55 a5 We11, ca1cu1ated (36Ar/38Ar)trapped ran9e5 fr0m 3.9 t0 4.3 1n the three 91a55 5amp1e5; a 51m11ar re5u1t wa5 06ta1ned 6y 5w1nd1e et a1. [5] f0r a f0urth 5amp1e. 7he 36Ar/35Ar rat10 1n the mart1an atm05phere wa5 0r191na11y e5t1mated fr0m V1k1n9 data t0 11e w1th1n the ran9e 4 - 7 [15]. A 1ater rep0rt [7] that th15 rat10 15 w1th1n •+ 10% 0f the terre5tr1a1 va1ue 0f 5.3 15 1nc0rrect [16]. 7he 11th0109y C trapped Ar c0mp051t10n, at the 10wer end 0f th15 ran9e, 15 theref0re n0t 1nc0n515tent w1th what 15 current1y kn0wn a60ut the mart1an Ar c0mp051t10n. 1f the trapped 36Ar/35Ar rat10 0f 4.1_+0.2 1ndeed repre5ent5 the mart1an atm05phere, and ref1ect5 a pr1m0rd1a1 va1ue, then mart1an ar90n 15 an0ma10u5 c0mpared t0 m05t 0f the kn0wn n0n5pa1109en1c re5erv01r5 1n the 501ar 5y5tem, wh1ch

have 36Ar/35Ar rat105 that d1ffer fr0m 5.3 6y at m05t a few percent. An except10n 15 a m1n0r n061e 9a5 c0mp0nent 1nferred 6y 81ack [17,18] fr0m 9a5-r1ch mete0r1te data and attr16uted t0 1mp1anted 501ar f1are 9a5e5, w1th 36Ar/35Ar = 4.1 • 0.8 and 2°Ne/22Ne = 10.6 •+ 0.3, very c105e t0 the va1ue5 ca1cu1ated here. 1t 15 unc1ear, h0wever, h0w the 6u1k 0f a p1anet•5 atm05pher1c n061e 9a5 1nvent0ry c0u1d 6e c0ntr16uted 6y 501ar f1are5 t0 the exc1u510n 0f 0ther 50urce5 5uch a5 501ar w1nd. M0re0ver, except f0r 36Ar/3~Ar, the e1ementa1 and 150t0p1c n0nrad109en1c n061e 9a5 pattern5 1n the mart1an and terre5tr1a1 atm05phere5 are 51m11ar en0u9h t0 p01nt t0 a c0mm0n 50urce [1]. 7heref0re a pr1m0rd1a1 d1fference 1n 36Ar/35Ar 5eem5 un11ke1y. An a1ternat1ve v1ew w0u1d 6e t0 a55ume that the pr1m0rd1a1 36Ar/35Ar rat10 wa5 1n fact c105e t0 terre5tr1a1-ch0ndr1t1c, 6ut ha5 6een m0d1f1ed 6y 50me p1anet-5pec1f1c pr0ce55. Preferent1a1 enr1chment 0f 38Ar 6y 9a1act1c c05m1c ray ( 6 C R ) 5pa11at10n 0f 5urface mater1a15 15 1n c0ncept an attract1ve p05516111ty, 51nce 5h1e1d1n9 0f the mart1an 5urface 6y even 5evera1 t1me5 the pre5ent atm05pher1c ma55 0f - 20 9 / c m 2 w0u1d 6e m1n0r f0r ener9et1c 9a1act1c pr0t0n5. H0wever, 1n deta11 th15 pr0ce55 pre5ent5 519n1f1cant pr061em5. 61ven the re9011th c0mp051t10n mea5ured 6y the V1k1n9 X R F exper1ment [19], and a55um1n9 the pre5ent-day 6 C R f1ux, the t1me re4u1red t0 chan9e the mart1an atm05pher1c 36Ar/35Ar rat10 fr0m 5.35 t0 4.1 w0u1d 6e - 35 × 10 9 year5 f0r the m05t fav0ra61e ca5e 1n wh1ch a11 the 5pa1109en1c ar90n wa5 50meh0w 0ut9a55ed fr0m the re9011th t0 the atm05phere. 7here w0u1d a150 have 6een a c0nc0m1tant 1ar9e pr0duct10n 0f 5pa1109en1c 21Ne, f0r wh1ch n0 ev1dence 15 5een 1n ana1y5e5 0f the EE7A 79001 91a55. 1t ha5 6een 5u99e5ted [9,20,21] that 1ar9e am0unt5 0f car60nate5 may have 6een dep051ted 0n the mart1an 5urface 1n the pa5t. 5pa11at10n 35Ar pr0duct10n rate5 1n ca1c1te are much 9reater, and 21Ne pr0duct10n rate5 much 1e55, than 1n the re9011th c0mp051t10n u5ed a60ve. H0wever, the t1me needed t0 9enerate the atm05pher1c 35Ar exce55 w1th the pre5ent 6 C R f1ux w0u1d 5t111 6e 0n the 0rder 0f 3 × 10 9 year5, even 1n the extreme ca5e 0f a p1anet-w1de 5urfac1n9 0f ca1c1te t0 a depth 0f > 2 meter5 and c0mp1ete re1ea5e 0f 5pa1109en1c 9a5e5 t0 the atm05phere. 7he 0n1y 0ther p05516111ty we can 1ma91ne t0

157

acc0unt f0r a 5pa11at10n 0r191n 0f the exce55 38Ar 1n 11th0109y C 15 the ad h0c a55umpt10n 0f 9a5 re1ea5e and c0ncentrat10n fr0m 10ca1, 1rrad1ated mater1a15 0n the p1anet•5 5urface dur1n9 the 5h0ck event, f0110wed 6y m1x1n9 w1th 1njected atm05pher1c 9a5e5. Here a9a1n the a65ence 0f exce55 21Ne re4u1re5 a tar9et chem15try d0m1nated 6y ca1c1um. 1n the ca5e 0f 5uch a 10ca112ed 0r191n f0r the exce55 38Ar, c0rrect10n5 f0r the a550c1ated 36Ar5p w0u1d 1ncrea5e (40Ar/36Ar) trapped 6y 5-6%. 5. 5ummary and c0nc1u510n5 7rapped n1tr09en 1n the EE7A 79001 91a55 pha5e 15 character12ed 6y 8~5N at 1ea5t a5 h19h a5 -300%0. 7w0 9a5 c0mp0nent5 are pre5ent, w1th 5amp1e-t0-5amp1e var1at10n5 1n the1r re1at1ve pr0p0rt10n5. N1tr09en 150t0p1c c0mp051t10n and the e1ementa1 rat105 36Ar/14N and 4°Ar/14N are c0var1ant a10n9 m1x1n9 11ne5 pa551n9 thr0u9h the mart1an atm05pher1c c0mp051t10n. Upward 1adder1n9 0f ~1~N re1ea5e pattern5 1n 5tepw15e heat1n9 re4u1re5 at 1ea5t tw0 k1nd5 0f 9a5 51te5 w1th d1fferent therma1 retent1v1t1e5, 0ne 0ccup1ed 6y 9a5e5 pre5uma61y trapped fr0m the mart1an atm05phere and the 0ther 6y a m0re m0611e c0mp0nent w1th 10w 315N. 8ecau5e Ar 1n th15 5ec0nd c0mp0nent 15 150t0p1ca11y 1nc0n515tent w1th the terre5tr1a1 c0mp051t10n and per515t5 t0 h19her temperature5 than expected f0r 51mp1e de50rpt10n, we c0nc1ude that m05t 0f 1t 15 11ke1y t0 6e 1nd19en0u5 t0 the 91a55 rather than der1ved fr0m the earth•5 atm05phere. 51nce n1tr09en t0 ar90n rat105 1n the m0611e c0mp0nent d0 n0t appear t0 vary, the n1tr09en 15 a150 a55umed t0 6e 1nd19en0u5. Mea5urement5 0f 15N/14N 1n 5NC mete0r1te5 6y 0ther w0rker5 [11] 5u99e5t that the 615N 1n th15 1nd19en0u5 9a5 may 6e a5 10w a5 - 35%0. F0r any 6~5N >1 300%0 1n the h19h-6~5N c0mp0nent, the am0unt5 0f th15 c0mp0nent ca1cu1ated t0 6e pre5ent 1n the 91a55 5amp1e5 are very un1f0rm, w1th var1a6111ty 1n the m1x1n9 rat10 due 0n1y t0 var1at10n 0f the 0ther c0mp0nent. F0r ~13Ntrappe d = +620%0 and 6 15 N1nd19. . . . . = --35%0, the c0mputed c0ncentrat10n 0f trapped N 1n each 0f the three 5amp1e5 15 84 pp6 t0 w1th1n + 5%. C0rre1at10n 11ne e4uat10n5 y1e1d 2260 + 200 f0r 4°Ar/36Ar 1n the trapped c0mp0nent, c0n515tent w1th the mart1an atm05pher1c mea5urement, a55um1n9 the 615N 0f th15 c0mp0nent 15 620 •+ 160%0.

7he 2°Ne/36Ar e1ementa1 rat10 1n C # 3 , and 84Kr/36Ar and 132Xe/36Ar rat105 mea5ured prev10u51y 1n C # 2 [1], a9ree w1th1n err0r w1th V1k1n9 va1ue5 f0r Mar5, a5 wa5 f0und 1n prev10u5 5tud1e5 0f EE7A 79001 91a55 [12]. 7h15 e1ementa1 c0mp051t10n 0f the n0nrad109en1c n0610 9a5e5 4ua11tat1ve1y re5em61e5 that 1n the earth•5 atm05phere. Ne0n 150t0p1c data 5u99e5t that 2°Ne/22Ne 1n the trapped 9a5e5 15 a150 c105e t0 the terre5tr1a1 rat10. H0wever, th15 51m11ar1ty t0 the terre5tr1a1 n061e 9a5 pattern d0e5 n0t extend t0 the n0nrad109en1c ar90n 150t0pe5: 36Ar/38Ar 15 - 25% 10wer 1n the EE7A 79001 trapped c0mp0nent than 1n the earth•5 atm05phere and ch0ndr1te5. 7he 0r191n 0f th15 unu5ua1 150t0p1c c0mp051t10n 15 an 0pen 4ue5t10n.

Ackn0w1ed9ement5 We thank the Mete0r1te W0rk1n9 6 r 0 u p f0r pr0v1d1n9 th15 5pec1a1 5amp1e 0f EE7A 79001 91a55, A.0. N1er f0r 111um1nat1n9 d15cu5510n5, and R. H111er and E. 8ackman f0r a5515tance 1n prepar1n9 the manu5cr1pt. We a150 thank the referee5, e5pec1a11y P. 519ner, f0r the1r he1pfu1 rev1ew5. 7h15 w0rk wa5 5upp0rted 6y NA5A 9rant N A 6 9-60.

Reference5 1 R.H. 8ecker and R.0. Pep1n, 7he ca5e f0r a mart1an 0r191n 0f the 5her90tt1te5: n1tr09en and n061e 9a5e5 1n EE7A 79001, Earth P1anet. 5c1. Lett. 69, 225-242, 1984. 2 D.D. 809ard, per50na1 c0mmun1cat10n. 3 A.0. N1er and M.8. McE1r0y, C0mp051t10n and 5tructure 0f Mar5• upper atm05phere: re5u1t5 fr0m the neutra1 ma55 5pectr0meter5 0n V1k1n9 1 and 2, J. 6e0phy5. Re5. 82, 4341-4349, 1977, 4 C.A. Pr0m60 and R.N. C1ayt0n, A 5pectacu1ar n1tr09en 150t0p1c an0ma1y 1n 8encu661n (a65tract), 1n: Lunar and P1anetary 5c1ence XV1, pp. 679-680, Lunar and P1anetary 1n5t1tute, H0u5t0n, 7exa5, 1985. 5 7.D. 5w1nd1e, M.W. Caffee and C.M. H0hen6er9, Xen0n and 0ther n061e 9a5e5 1n 5her90tt1te5, 6e0ch1m. C05m0ch1m. Acta, 1n pre55, 1986. 6 7. 0wen and K. 81emann, C0mp051t10n 0f the atm05phere at the 5urface 0f Mar5: detect10n 0f ar90n-36 and pre11m1nary ana1y515, 5c1ence 193, 801-803, 1976. 7 7. 0wen, K. 810mann, D.R. Ru5hneck, J.E. 8111er, D.W. H0warth and A.L. Laf1eur, 7he c0mp051t10n 0f the atm05phere at the 5urface 0f Mar5, J. 6e0phy5. Re5. 82, 4635-4639, 1977. 8 D.W. Muen0w and J.L. 600d1n9, ••Mart1an•• v01at11e5 1n 5her90tt1te EE7A 79001: p055161e 519n1f1cance 0f 5ec0ndary m1nera15 (a65tract), 1n: Lunar and P1anetary 5c1ence XV1, pp. 593-594, Lunar and P1anetary 1n5t1tute, H0u5t0n, 7exa5, 1985.

158 9 E. Ander5 and 7. 0wen, Mar5 and Earth: 0r191n and a6undance 0f v01at11e5, 5c1ence 198, 453-465, 1977. 10 7.D. 5w1nd1e, M.W. Caffee, C.M. H0hen6er9, 6 . 8 . Hud50n and R.5. Rajan, N061e 9a5e5 1n 5NC mete0r1te5 (a65tract), 1n: Mete0r1t1c5 19, 318 319, 1984. 11 A.E. Fa111ck, R.W. H1nt0n, D.P. Mattey, 5.J. N0rr15, C.7~ P1111n9er, P.K. 5wart and 1.P. Wr19ht, N0 unu5ua1 c0mp051t10n5 0f the 5ta61e 150t0pe5 0f n1tr09en, car60n and hydr09en 1n 5NC mete0r1te5 (a65tract), 1n: Lunar and P1anetary 5c1ence X1V~ pp. 183-184, Lunar and P1anetary 1n5t1tute, H0u5t0n, 7exa5, 1983. 12 D.D. 809ard, L.E. Ny4u15t and P. J0hn50n, N061e 9a5 c0ntent5 0f 5her90tt1te5 and 1mp11cat10n5 f0r the mart1an 0r191n 0f 5NC mete0r1te5, 6e0ch1m. C05m0ch1m. Acta 48, 1723-1739, 1984. 13 J.8. P011ack and D.C. 81ack, N061e 9a5e5 1n p1anetary atm05phere5:1mp11cat10n5 f0r the 0r191n and ev01ut10n 0f atm05phere5, 1caru5 51, 169-198, 1982. 14 D. Y0rk. Lea5t 54uare5 f1tt1n9 0f a 5tra19ht 11ne, Can. J. Phy5. 44. 1079-1086, 1966. 15 K. 81emann, 7. 0wen, D.R. Ru5hneck, A.L. Laf1eur and D.W. H0warth, 7 h e atm05phere 0f Mar5 near the 5urface: 150t0p1c rat105 and upper 11m1t50n n061e 9a5e5, 5c1ence 194, 76-78, 1977. 16 7. 0wen, Update 0f the Ander5-0wen m0de1 f0r mart1an v01at11e5 (a65tract), 1n: LP1 7echn1ca1 Rep0rt 0n the Ev01ut10n 0f the Mart1an Atm05phere. Lunar and P1anetary 1n5t1tute, H0u5t0n, 7exa5, 1n pre55, 1986. 17 D.C. 81ack, 7rapped ne0n-ar90n 150t0p1c c0rre1at10n5 1n 9a5-r1ch mete0r1te5 and car60nace0u5 ch0ndr1te5, 6e0ch1m. C05m0ch1m. Acta 35, 230-235, 1971. 18 D.C. 81ack, 0 n the 0r191n5 0f trapped he11um, ne0n, and ar90n 150t0p1c var1at10n5 1n mete0r1te5, 1. 6a5-r1ch mete0r1te5, 1unar 5011, and 6recc1a, 6e0ch1m. C05m0ch1m. Acta 36. 347-375, 1972. 19 8.C. C1ark, A.K. 8a1rd, H.J. R05e, Jr., P. 70u1m1n 111, R.P. Chr15t1an, W.C. Ke111her, A.J. Ca5tr0, C.D. R0we, K. Ke11 and 6 . R . Hu55, 7 h e V1k1n9 X-ray f1u0re5cence exper1ment: ana1yt1ca1 meth0d5 and ear1y re5u1t5, J. 6e0phy5. Re5. 82, 4577-4594, 1977. 20 J.8. P011ack, C11mat1c chan9e 0n the terre5tr1a1 p1anet5, 1caru5 37, 479-553, 1979. 21 R. Kahn, 7 h e ev01ut10n 0f C02 0n Mar5, 1caru5 62, 175-190, 1985.

22 E. Ma20r, D. H e y m a n n and E. Ander5, N061e 9a5e5 1n car60nace0u5 ch0ndr1te5, 6e0ch1m. C05m0ch1m. Acta, 34, 781 824, 1970. 23 C.-C. Kun9 and R.N. C1ayt0n, N1tr09en a6undance5 and 150t0p1c c0mp051t10n51n 5t0ny mete0r1te5, Earth P1anet. 5c1. Lett. 38, 421 435, 1978. 24 J. Cra66 and E. Ander5, N061e 9a5e5 1n E-ch0ndr1te5, 6e0ch1m. C05m0ch1m. Acta 45, 2443-2464, 1981. 25 L. 5chu1t2 and H. Kru5e, L19ht n061e 9a5e5 1n 5t0ny mete0r1te5--a c0mp11at10n, Nuc1. 7rack Detect• 2, 65-103, 1978. 26 Unpu6115hed M1nne50ta data. 27 5.J. N0rr15, P.K. 5wart, 1.P. Wr19ht, M.M. 6 r a d y and C.7. P1111n9er, A 5earch f0r c0rre1ata61e, 150t0p1ca11y 119ht car60n and n1tr09en c0mp0nent5 1n 1unar 50115 and 6recc1a5, Pr0c. 14th Lunar P1anet. 5c1. C0nf., J. 6e0phy5. Re5. 88, 5upp1. 8200-8210, 1983. 28 U. Fr1ck and R.0. Pep1n, 5tudy 0f 501ar w1nd 9a5e5 1n a y0un9 1unar 5011 (a65tract), 1n: Lunar and P1anetary 5c1ence X11. pp. 303-306, Lunar and P1anetary 1n5t1tute, H0u5t0n. 7exa5, 1981. 29 W. H~6ner, 7. K1r5ten and J. K1k0, Rare 9a5e5 1n Ap0110 17 50115 w1th empha515 0n ana1y515 0f 512e and m1nera1 fract10n5 0f 5011 74241, Pr0c. 6th Lunar 5c1. C0nf., pp. 2009 2026. 1975. 30 P. E6erhardt, 0. Eu95ter, J. 6e155. N. 6r/591er, 5. 6u99156er9, and M. M13r9e11, N061e 9a5e5 1n the Ap0110 16 5pec1a1 50115 fr0m the Ea5t-We5t 5p11t and the permanent1y 5had0wed area, Pr0c. 7th Lunar 5c1. C0nf., pp. 563 585, 1976. 31 R.0. Pep1n, J.R. 8a5f0rd, J.C. Dra90n, M.R. C05c10, Jr. and V.R. Murthy, Rare 9a5e5 and trace e1ement5 1n Ap0110 15 dr111 c0re f1ne5: Dep051t10n chr0n01091e5 and K-Ar a9e5, and pr0duct10n rate5 0f 5pa11at10n-pr0duced - He, ~ Ne, and 35Ar ver5u5 depth. Pr0c. 5th Lunar 5c1. C0nf., pp. 2149-2184. 1974. 32 R.H. 8ecker and R.N. C1ayt0n, N1tr09en 150t0pe5 1n 1unar 50115 a5 a mea5ure 0f c05m1c-ray exp05ure and re9011th h15t0ry, Pr0c. 8th Lunar 5c1. C0nf., pp. 3685-3704, 1977. 33 R,N. C1ayt0n and M.H. 7h1emen5, Lunar n1tr09en: Ev1dence f0r 5ecu1ar chan9e 1n the 501ar w1nd, 1n: Pr0c. C0nf. Anc1ent 5un, R.0. Pep1n, J.A. Eddy, and R.8. Merr111, ed5., pp. 463 473, Per9am0n, 1980.