chemical analyses and diffusion studies of gases in andesitic lavas

8/13/2019 Chemical Analyses and Diffusion Studies of Gases in Andesitic Lavas

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Che mtca l Geology,61 1987) 299-308 299Elsewer Scmnce Pubhshers B V, Amsterdam -- Printed m The Netherlands

C H E M IC A L A N A L Y S E S A N D D IF FU SIO N S T U D IE S O F G A S E S

IN A N D ES I TIC LAVA S A R EN A L V O LC A N O ( C O S TA R IC A )*

J L Z I M M E R M A N N 1, J L C H E M I N E E 2 ~a nd H D E L O R M E ~4

~Centre de Re cher che s Pdtrograph ~ques et Gdoch~m~ques, F-54501 Vando euvre-les-Nanc:~ C~dex (Fr an ce)~Laboratotre de Gdolog~e, ]Ecole No rm ale Su per leur e, F -75005 Parl~ Cddex (Fr an ce)

~Observato~res Volcanolog~ques, I P G P , F-7523 0 Par~s Cedex 05 (F ran ce)4Laborato~re de Geoch~rn~e des Isotop es Stables, F-7 5000 P ar ~ Cddex 05 (F ran ce)

Accept ed for pubhc atmn July 11, 1986 )

A b s t r a c t

Zlmm erma nn, J L , Chemm~e, J L and Delorme, H , 1987 Chemmal analyses and dfffusmn studms of gases m andes-1tic lavas Arenal Volcano Costa Rlca) In E E Horn and J -J Behr Guest- Editor s), Current Research on FluidInclusmns, EC RFI , Gottl ngen, April 10-12, 1985 Chem Geo l, 61 299-308

Early m 1981, the eruptive behavi or of the Arenal Volcano changed - an essentially effuswe period was mterrup tedby an exploswe phase Analyses by mass spect romet ry of occluded gases H~O, C02, CO, N,, H2 and CH4) m lavasamples both younger and older than t he exploswe event were carried out Although the fluid phases have approxi-mately the same composition, the more recent lavas are enrmhed m gases relative to the older ones Dehydratmn takesplace at temperat ures ~ 50 ° C higher for the older lavas Dist ract ive H20 and CO2 dfffusmn hnes and CO / CO + CO, )ratms 0 35 and 0 30, respectwely), for both lava types substantmte this difference Some orgamc compounds are alsopresent m all samples albeit m small quantltms

1 I n t r o d u c t i o n

E x h a l a t e d g a s a n a l y s i s ~ s o n e o f t h e p r i n c i p a lm e t h o d s t o d e t e r m i n e t h e c o m p o s l t m n o f m a g -m a t in f l u id s T h e s e f l u i d s c o r r e s p o n d t o t h ec o m p o s i t i o n o f t h e f r a c t m n e x s o l v e d a t t h e t im e

o f a c t i v it y H o w e v e r , t h e y a r e o f t e n c o n t a m i -n a t e d w i t h g r o u n d w a t e r a n d a t m o s p h e r i c g a se sa n d m u s t b e c o l l e ct e d d i r e c tl y a t t h e v e n t s I ns o m e c a s e s , t h e a c c e s s t o t h e v e n t s i s d i f f i c u l t ,o r ~ m p o s s i b l e , d u e t o v o l c a n i c a c t i v i t y G a s e se n t r a p p e d i n v o lc a n i c r o c k s a r e a ls o r e p r e s e n t -a t lv e o f m a g m a t l c f lu i d s a n d m a y r e f le c t th eP T fo2 c o n d i ti o n s m a m a g m a c h a m b e r

*Contr~butmn C R P G No 692

H o w e v e r , t h e s e g a s e s ar e p r e s e n t m v e r y lo wq u a n t i t i e s , c o n t r a r i l y t o s a m p l e s f r o m v e n t a r e a si n e r u p t i v e p e r i o d s , t h e l a v a s a r e a l w a y sa c c e s s t b l e

M a s s s p e c t r o m e t r y ( w i t h ~ ts h i g h s e ns lt ~ v -l t y ) is o n e o f t h e m o s t u s e d m e t h o d s t o s t u d y

t h e s e m a g m a t l c v o l a h l e s ( Z l m e r m a n n , 1 9 72 ,B a r k e r a n d S o m m e r, 1 9 7 3 , H d k m l a n e t a l, 1 9 7 3,K l l h n g l e y a n d M u e n o w , 1 9 7 4 , 19 7 5, P r m e e t a l ,1 9 7 7 , D e l a n e y e t a l , 1 9 7 8 , M u e n o w, 1 9 7 9 ,C h a l g n e a u e t a l , 1 9 80 , Z i m m e r m a n n e t a l ,1 9 8 1 ) T h i s e x p e r i m e n t a l p r o c e d u r e h a s s o m em c o n v e m e n c e s , e g t h e c o m p l e x i t y o f t h e g a sm i x t u r e a l w a y s g ~v es m a s s i n t e r f e r e n c e s F u r -t h e r m o r e , h e a t i n g m a y b r i n g a b o u t d i s so c l a-t m n s , r e - e q u l h b r a t m n s a n d r e a c t m n s b e t w e e n

0009-2541/87 / 0350 © 1987 Elsevmr Scmnce Pubhs hers B V



301

TAB LE I

Molar com posl tmns of released fired phase heati ng at 1200 ° C during 3 5 h)

ample H2 0 C02 CO N~ H2 CH4 SO

( ~ ( ) ( ) ( ) ( ) ( )

Orgamc

compounds*

AR 7 9 6 67 3 20 2 10 9 1 5 0 06 0 01 tr , •AR 8 0 8 68 1 19 4 10 7 1 6 0 09 0 01 * *AR 8 1 1 63 5 24 0 10 8 1 6 0 06 0 01 • *AR 8 1 2 65 7 22 8 9 8 1 5 0 08 0 02 • * *

*Unqu antlf led gases * -- few, ** = mos t)

f o r t h e f o u r f l o w s ( T a b l e I ) I t i s f o r m e d e s s e n -t ia l ly o f w a t e r ( ~ 6 4 - 6 8 ) a n d c a r b o n o x i d e s( C O 2 ~ 1 9 - 2 4 , C O - ~ 1 0 ) , a n d s o m e o t h e rg a s es , m o s t l y m t r o g e n ( N 2 ~ 1 5 ) H y d r o g e n ,m e t h a n e , o r g a n i c c o m p o u n d s a n d s u l p h u rd l o m d e a re f o u n d a s t r a c e s O r g a m c c o m -p o u n d s c a n n o t b e i d e n t if i e d ( o n l y C H 4 c a n b em e a s u r e d , a n d C 2 H 2, C2 H 4 , C 2 H 6 a n d C 3 H 6i d e n t i f i e d w i t h o u r m a s s s p e c t r o m e t e r , t h e i rq u a n t i t a t i v e a n a l y s i s i s s p e c u l a t i v e b e c a u s e o fm a s s i n t e r f e r e n c e s m t h e s o u r c e o f t h e m a s ss p e c t r o m e t e r , b u t t h e i r e x i s t e n c e i s r e v e a l e d b ys o m e o f t h e i r c r a c k i n g p r o d u c t s , m p a r t i c u l a rm e t h y l r a d ic a l E l e m e n t a l o r g a n i c a n a l y s e s

p e r f o r m e d a t t h e C e n t r e d e P d d o l o g i e B i o l o -g xq ue ( N a n c y ) g iv e c a r b o n c o n t e n t s f r o mo r g a n ic c o m p o u n d s b e t w e e n 0 0 1 5 a n d 0 0 5w t a n d n i tr o g e n c o n t e n t s o f ~ 0 0 0 4 w tWa t e r a n d c a r b o n d i o x i d e m e a s u r e m e n t s b ym a s s s p e c t r o m e t r y a n d b y c h e m i ca l m e t h o d s( K a r l - F i s c h e r f o r H 2 0 , c o u l o m e t r y f o r C O 2 )s h o w f e w d if f e r e n c e s b e t w e e n t h e f o u r s a m p l e s( Ta b l e I I ) N e v e r t h e l e s s , t h e r e is a s y s t e m a t i -c a l i n c r e a se o f H 2 0 a n d C O 2 c o n t e n t s m t h eJ u n e 1 9 81 s a m p l e s f o r w h m h t h e v o l c a n o a c t iv -i ty w a s m o r e e x p l o s i v e T h e s e a n a l y t i c a l r e s u l t sa r e v e r y d i f f e r e n t fr o m t h e s u p p o s i t i o n s o fN e w h a l l a n d N e l s o n ( 1 9 8 3 ) b a s e d o n ch e m i c a la n a l y s e s o f m a j o r e l e m e n t s

I n c r e m e n t a l h e a t i n g a n a l y s i s a l lo w s to c o m -p a r e t h e r e le a s e h i s t o g r a m s o f t h e p r i n c i p a lg a se s H y d r o g e n a n d m e t h a n e r e le a se o cc u r sm a i n l y b e t w e e n 3 0 0 ° a n d 8 0 0 ° C , w h i l e t h er e le a s e o f o t h e r g a s e s ( H 2 0 , C Q , C O a s t h em o s t a b u n d a n t ) a r e m o r e s p r e a d u n t i l 1 2 0 0 ° C ,

w i t h a s t r o n g e r i n t e n s i t y f r o m 4 0 0 ° to 1 0 0 0 ° CC o n t i n u o u s a n d l i n e a r h e a t i n g c u r v e s ( h e a t -

m g r at e 4 0 0 ° C h - l ) a ll ow t o c o m p a r e h b e r a-t l o n o f ea c h g a s m t h e d i f f e r e n t s a m p l e sw h a t e v e r t h e i r g a s e s c o n t e n t s a r e , a c c o r d in g

Q/Qo =[ T)w h e r e Q = r e l e a s ed q u a n t i t y f r o m h e a t i n g s t a r tt o T ( ° C ) , a n d Q o = t o t a l r e l ea s e d q u a n t i t ya s s u m e d t o b e c lo s e t o t h e i n i ti a l q u a n t i t y m t h es a m p l e

F o r w a t e r ( F i g l a ) , t h e c u r v e s a r e t h e s a m ef o r l a v a s o f J u n e 1 9 7 9 a n d A p r i l 1 9 8 0 , b u t t h e s ea r e m o v e d f o r w a r d b y ~ 5 0 ° C f o r l a v a s o f J u n e

1 9 81 M o r e o v e r t h e y h a v e t w o i n fl e c ti o n p o i n ts ,t h e f i rs t n e a r 6 0 0 ° C , a n d t h e s e c o n d b e t w e e n1 0 5 0 ° a n d 11 5 0 ° C ( r a n g e o f t h e e m i t t e d l a v af l o w t e m p e r a t u r e s , C l g o h m e t a l , 1 9 8 4 ) T h e s ei n d i c a te p e r h a p s t h r e e s i te s fo r w a t e r a d s o r p -t i on , ( < 600 ° C) , b ub b l e s ( < 1000 ° C ) and so l i dso l u t i on m g l a s se s ( > 1000 ° C )

L i b e r a t i o n c u r v e s o f c a r b o n d i o x i d e a re s i m -i la r f o r t h e f o u r s a m p l e s ( F i g l b ) a n d a l s o f o rh y d r o g e n ( F ig l c ) a n d m e t h a n e ( F i g l d )T h e s e g a s es a r e r e le a s ed b e f o r e l l 0 0 ° C H o w -e v e r , t h e r e i s a n r e f l e c t i o n p o i n t a t ~ 6 0 0 ° C f o rt h e m e t h a n e c u r v e , w h i c h c a n i n d i c a te a d is s o -c i a ti o n o f h e a v i e r h y d r o c a r b o n s

5 D i f f u s i o n o f g a s e s

I f g a s r e l e a s e i s c o n s i d e r e d a s d i f f u s i o n , i t i sc h a r a c te r iz e d b y t h e A r r h e n m s e q u a t io n

D = D o e xp ( - E / RT )



302

w h e r e D = d f f fu s m n c o e f fi c m n t(cm 2 s - - l ,D o = d l ff u s x o n c o n s t a n t , E = a c t l v a t m n e n e r g y

k c a l m o l - ~ ) , R = u m v e r s a l g a s c o n s t a n t , a n dT = a b s o l u te t e m p e r a t u r e

A s s u m i n g s p h e r i c a l g r a m s , i n c r e m e n t a lh e a t i n g a n a l y s a s a l l o w s t o c a l c u l a t e D a n d Eu s i n g t h e C a rs l aw a n d J a e g e r 1 9 5 9) e q u a t m n

F= Qo-Q)/Qo

-1 6- ~ ~ n - 2 e x p [ - n 2 r c 2 D t / a 2 ) ]n = l

w h e r e F= f r a c t io n a l l o ss o f g a s, a - - r a d m s o fs u p p o s e d sp h e r ic a l g ra m s , a n d t = t a m e o fh e a t i n g

W h e n t h e r e ~s d f f f u s m n , t h e f o l l o w i n g e q u a -taon as l inea r

l og D/a 2 log Do/a 2 E/ R T

= c o n s t - E / R T

T h e s l o p e s o f t h e s t r m g h t l an e s a n l o gD/a zv s 1/T p l o t s g a ve t h e a c t x v a t m n e n e r g y f o r t h e

h b e r a t l o n o f t h e s t u d m d g as F o r w a t e r Ta b l eI I I ) , t h e r e a r e t w o s t r a ig h t h n e s F i g 2 ) T h ef i r st o n e c o r r e s p o n d s t o t h e f i r st s t e p s i n c l u d i n gt h a t o f 5 0 0 ° C , t h e s e c o n d r a n g e s f r o m t h e 6 0 0 ° C

s t e p t o t h e 1 0 0 0 ° C s t e p w i t h a c t x v a t x o n e n e r -g in s o f 1 0 + 2 a n d 1 6 + 2 k c a l m o l 1, r e s p e c -t a v el y T h e s e v a l u e s a p p l y t o t h e f i r s t t w o p a r t so f t h e c o n t i n u o u s d e h y d r a t m n c u r v es a n d c o r -r e s p o n d t o d i f f e r e n t s o l u t m n m e c h a m s m sa l l u d e d to a b o v e , t h e t h a r d c a n n o t a p p e a r h e r eb e c a u s e th e r e Is o n l y o n e st e p 1 2 0 0 ° C ) a f t e rt h e o n e o f 1 0 0 0 ° C A s s u m m g g r a m s w a th ad t a m e t e r o f 1 m m , c o m p u t e d d a f f u s x o n c o e f f i -c m n t s a r e b e t w e e n 1 0 a3 a n d 1 0 - 1 2 c m 2 s 1 f o r1 1 m m , 1 2 1 - 1 0 - 13 c m 2 s - a ) M o r e o v e r , t h e s es t r m g h t h n e s F i g 3 ) a ll o w u s t o d a s t m g u x s ht w o l a v a f a m f l m s 1 ) J u n e 1 9 7 9 a n d A p r il 1 9 8 0l a v a s, a n d 2 ) J u n e 1 9 8 1 l a v a s

F o r c a r b o n d m x l d e Ta b l e I V ) , t h e l ogD/a 2v s 1/T e x p r e s s x o n g i v e s o n l y o n e s t r m g h t l a n ef o r e a c h l a v a f lo w F i g 3 ) T h e s e fo u r s t r m g h th n e s c a n b e a ls o g r o u p e d t o g e t h e r m t w o f a m l -h e s 1 ) J u n e 1 9 79 a n d A p n 11 9 8 0 , a n d 2 ) J u n e

TABLE II

Water and C02 contents (m gramme per cent) measured by different experimental processes

Extractmn, Ar 79 6 Ar 80 8 AR 81 1analysis

AR 81 2

H20 C02 H20 C02 H20 C02 H20 C O

(g ) (g ) (g ) (g ) (g ) (g ) (g ) (g )

Heating at 1200°C,grams ~ 1 mm, MS 0 083 0 061 0 078 0 054 0 091 0 083 0 092 0 078

Continuous heating

from 120 ° to 1220°C,grams ¢ 1 mm, MS 0 093 0 047 0 083 0 044 0 092 0 065 0 096 0 066

Glass ¢ ~< 0 2 mm1200°C, MS

Grams ~ 1 mm, 0 060 0 030 0 052 0 031 0 068 0 054 0 087 0 068

Karl-Fischer (HeO)coulometmc (C02)analyses 0 080 0 050 0 070 0 060 0 090 0 060 0 095 0 080

Analytic methods MS, mass spectrometry, (HeO, CO:), Karl-Fischer (H20), coulometry (C02)Errors H20, 3 , C02, 2Permds ofsamphng AR 79 6 June 1979, AR 80 8 April 1980, AR 81 1 June 1981, Ar 81 2 June 1981



303

Q / Q o

2 0 0

t

I

.

~) +.

+

H 2 \ '

* + •

• A R 7 9 - 6÷ A R 8 0 - 8

+ " ~ * A R 8 1 - 1+ l~ , • ~ + A R 8 1 - 2

" ; * * T e m p e r a t u r e ° CL i

4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0

Q / Q o

0

2 0 0

.

+

• C O 2+

•+ T e m p e r a t u r e ° CI,

4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0

Q / Q o

o

o

o

t

H 2

+

+ •

• T e m p e r a t u r e ° CI I , ÷~ , I 1 2100 1-

2 0 0 4 0 0 6 O O 8 0 0 1 0 0 0

0 5

Q / Q o1

0 k ~2 0 0

\

+×

+~

L

4 0 0 6 0 0

t

*: CH4

//

T e m p e r a t u r e ° CJ

8 0 0 1 0 0 0 1 2 0 0

F i g 1 C o n t i n u o u s a n d l i n e a r h e a t i n g a n a l y s e s L i b e r a t i o n c u r v e s o f a ) H 2 0 , b ) C O , , c ) H 2 , a n d d ) C H 4 H e a t i n g r a teo f 6 6 6 °CmIn ]

1 9 8 1 T h e i r a c t l v a t m n e n e r g m s ar e 12 a n d 1 0k c a l m o l 1, r e s p e c t i v e l y T h e i r d i f f u s i o n c o e f -f i c m n t s a t 2 0 ° C a r e n o t v e r y d i f fe r e n t f r o mt h o s e fo r H 2 0 T h e s e v a l u e s ar e c o m p a r a b l e t ot h o s e o b t a i n e d o n b a s a l t i c l a v a s fr o m A r d o u -k S b a, A f a r ( Z l m m e r m a n n e t a l , 1 9 8 1 )

6 . O r i g i n o f C 0 2 , C O , C a n d o r g a n i cc o m p o u n d s

C a r b o n d i o x id e w h o s e c o n t e n t i s c o m p r i s e db e t w e e n 0 0 5 a n d 0 0 8 w t i s n e x t t o w a t e r t h em o s t a b u n d a n t g a s i n t h e s e l a v a s A s fo r w a t e r



T A B L E I V

D i f f u si o n c h a r a e t e n s t m s o f C O 2 C a r s l a w a n d J a e g e r m e t h o d )

3 0 5

S a m p l e A R79 6 A R 8 0 - 8 A R81 1

T F D/a 2 F D/a 2 F D/a 2

(*C ) ( ) (10--7 S 1) ( ) lO-V s -~ ) ( ) (10 7s 1)

A R 81 2

F D/a e

( ) 1 0 7 s 1)

2 0 0 1 5 0 0 1 6 3 4 0 0 3 6 1 6 0 0 2 0300 4 1 0 12 7 0 0 31 10 2 0 334 0 0 1 0 3 0 3 4 11 8 1 0 2 2 7 3 25 0 0 1 3 0 0 9 7 2 4 7 4 0 3 3 3 7 36 0 0 1 6 2 2 0 3 1 3 6 4 5 3 3 2 27 0 0 2 4 9 2 0 3 8 3 1 3 6 5 8 4 98 0 0 2 9 4 5 6 4 4 5 1 6 8 2 3 1 0 09 0 0 3 3 6 9 6 5 5 2 2 7 9 3 2 1 35

1 ,0 0 0 5 4 0 1 3 7 4 1 3 1 9 5 6 1 6 01 , 2 0 0 1 0 0 1 0 0 1 0 0

3 1 0 0 5 11 0 0 0 3 21 5 5 1 42 2 5 4 04 2 1 1 2 54 9 9 2 16 3 1 4 48 4 7 8 68 9 7 1 2 5

1 0 0

F = r e l e a s e d f r a c t i o n ,D/a 2 = d f f f u s m n c o e f f m m n t , w a t h a = r a d m s o f s u p p o s e d s p h e r i c a l g r a m s

~ L o g D / a 2

C O 2

• A R 7 9 6x

I 4 - x • A R S 0 8x

l

x A R 8 1 - 1+

+ + AR 8 1 2• +

• x

i

~ o - o

3 5 1 0 1 ) 2 1o 1 0 ~ O / T

F xg 3 D f f f u s m n o f C 0 2 C a r s l a w a n d J a e g e r m e t h o d ) , l ogD/a 2 v s 1 0 0 0 / T S a m e e x p l a n a t i o n as f o r w a t e r F i g 2 )

carbon dioxide within the extr actm n lineWhat is the origin of orgamc compounds

whose existence is proven by CH4 and crackingpeaks m mass spectra 9 Thexr presence isreported m meteorites Anders et al, 1973) andm alkahne igneous rocks Petersflxe andS6rensen , 1970) In basalts, Muenow 1973)heating tholentlc glass from Hawan hasobtained mass spectra char acten stm of crack-mg of orgamc constituents, It seems probablethat most of these orgamc compounds are

entrapped during nsmg and effusion of mag-matxc material through hthosphere and bms-phere Thxs hypothesis is suggested by theheterogeneous distribution of organic mat ter manalysed grains Unless they were formed fromcarbon, hydrogen, nitrogen and oxygen per-oxxde groups ) react ions at t he lava surface dur-

ing the eruption Freund, 198 1 and oralcommunic ation, Nancy, May 1984) or duringheatin g of samples m the laborator y In thiscase, thxs would explain the forma tion of part

probably minor quantities) of the water andcarbon oxides Met han e which is stable at hightemperature and pressure with low oxygenfugaclty may belong to the initial gases andcould be from mant le on gm Gold, 1982) Thesame process Is possible for hydro gen

However m this study, it is difficult to choosebetween the hypotheses concerning the ongmof hydrogen Taylor et al, 1983) and methanein volcanic rocks Isotopic geochemistry ofhydrogen and carbon Pmea u et al, 1976,Delorme et al , 1981; Javo y et al, 1982, Delorme,1983) shows tha t water m t he f umaroh c gasescollected on the dome of Arenal in 1979 and 1980is from mete oric origin, whereas the 613C-valueis slightly heavier th an magmatlc values



306

kbar

/r COl CO+C02 /

~J~ / / / / ~ / /

TJ L

Fig 4 Mola r compos: tmn o f vapor m C02- C0 sys tem meqmhbrmm with C, ca lcula ted f rom modif ied Red-dhch-K wo ng thermodynamm functaons Hol loway, 1977 )

7 . C 0 2 C O a n d C e q u i l i b r i u m

A s s u m i n g t h a t C 0 2 , C O a n d C a r e m l t m l l yp r e s en t , e q m h b r m m b e t w e e n c a r b o n a n d a C O

v a p o r c o u l d b e g o v e r n e d b y t h e B o u d o u a r dr e l a t i o n

C O 2 + C ~ - 2 C O

T h e m o d ff m d R e d d h c h - K w o n g ( M R K )t h e r m o d y n a m i c f u n c t io n s ( H o l l o w a y, 1 9 77 ,E g g l e r e t a l , 1 9 7 9 ) a l lo w t o re l a t e t e m p e r a t u r e ,p r e s s u r e a n d m o l a r c o m p o s i t i o n o f t h e v a p o rp h a s e ( F i g 4 ) A n a l y s e s o f t h e f lu i d p h a s ee x t r a c t e d m o n e 1 2 0 0 ° C s t e p ( Ta b l e I ) g iv e ar a t m C O / ( C O + C 0 2 ) o f 0 3 5 f o r t h e J u n e 1 9 79and Apr i l 1980 lavas an d a r a t i o o f 0 30 f o r t hos eo f J u n e 1 9 81

I f t h e p r e s s u r e i s 2 5 k b a r ( 8 k m d e e p ), r a t m so f 0 35 a n d 0 3 0 c o r r e s p o n d t o a t e m p e r a t u r e o f11 2 5 ° a n d 1 0 8 0 ° C , r e s p e c t i v e l y W i t h a p r e s -s u re o f o n l y 1 k b a r ( 3 k m d e e p ) , t e m p e r a t u r e sa r e r e s p e c t i v e l y o f 1 0 8 0 ~ a n d 1 0 4 0 ° C Va l u e sa r e c lo s e t o t h o s e o f t h e l a s t m f l e c t m n p o i n t o nc o n t i n u o u s d e h y d r a t i o n cu r v e s ( F i g 2 a )M o r e o v e r , t h e r a n g e o f m e a s u r e d e x t r u s i o n

t e m p e r a t u r e s i s b e t w e e n 11 0 0 a n d 11 5 0 cC( C l g o h m e t a l , 1 9 8 4 )

N e v e r t h e l e s s t h e c o r r e s p o n d i n g o x y g e nf u ga c ~t y ~s m u c h l o w e r t h a n t h e e s t i m a t e d o n e

m t h e g a s e s s a m p l e d a t th e s u r f a c e ( D e l o r m e ,1 9 8 3 ) T h e e x c e s s o f C O o v e r t h a t w h i c h s h o u l db e p r e s e n t f o r hx g h er o x y g e n f u g a c l tm s m a y b ea t t r i b u t e d t o r e a c t m n s m t h e e x t r a c t m n h n eT h i s c o u l d a l s o e x p l a i n t h e e x i s t e n c e o f lo wa m o u n t o f h y d r o c a r b o n s

8 . C o n c l u s i o n s

D e s p i t e o f a l m o s t s x m fl ar c o m p o s x t :o n o f th e x rg a s p h a s e s , t h e s e f o u r l a v a s f o r m t w o d x s t m c tg r o u p s

( 1 ) J u n e 1 9 7 9 a n d A p r i l 1 9 8 0 la v a f l o w s , w i t hq u i e t e m x s s : o n

( 2 ) J u n e 1 9 8 1 l a v a f lo w a n d J u n e 1 9 8 1 b o m b ,w ~ t h e x p l o s i v e a c t i v i t y

T h e s e c o n d g r o u p c o n t a i n s s l i g h t l y m o r ef lu i d s t h a n t h e f i rs t f r o m 0 0 9 - 0 1 0 H 2 0 a n d0 0 7 - 0 0 8 C O 2 t o 0 0 8 H 2 0 a n d 0 0 5 C 0 2

T h e i r c o n t i n u o u s d e h y d r a t i o n c u r v e s a re a ls od i f f e r e n t , w i t h a n i n t e r v a l o f - - 5 0 : C t o w a r d st h e h i g h e r t e m p e r a t u r e f o r t h e f i r st

B e s i d e s th e i r H e O a n d C 0 2 d i f fu s i o n A r r h e -n m s p l o t s l o gD/a 2 v s 1 / T a l s o m d x c a t e t w of a m l h e s T h e s e a r e al s o c o n f i r m e d b y t h e i rC O / ( C O + C O ) ) r a t io s 0 3 5 a n d 0 3 0 fo r th ef i rs t a n d s e c o n d g r o u p , r e s p e c t iv e l y T h e s er a t i o s c o u l d c o r r e s p o n d t o a n e q u x h b r m m t e m -p e r a t u r e b e t w e e n C O 2, C O a n d C o f 112 5 ~ a n d1 0 8 0 ° C , r e s p e c t i v e l y, a t a p r e s s u r e o f 2 5 k b a r

T h e e s t ~ m a h o n o fP T c o n d l t m n s ~s c e r -t a i n l y q u i t e ~ m p r e o s e a s y e t a n d f a r f ro m t h eo x y g e n f u g ac ~ ty v a lu e s d e t e r m i n e d m s u r f a c ef r o m s a m p l i n g m th e v e n t s ( D e l o r m e , 1 9 8 3 )

A c k n o w l e d g e m e n t s

F P m e a u g a v e b a s a l t ic g l a s se s w i t h w a t e rc o n t e n t s a n a l y s e d w i t h h ig h p r e c is : o n a n d c n t -



lc ~z ed t h e m a n u s c r i p t M S e m e t i m p r o v e d t h eE n g h s h a n d d i s c u s s ed a l so t h e m a n u s c r i p t FL h o t e c a r ri ed o u t t h e X - r a y a n a l y s e s M Ve r -n e t d e t e rm i n e d t h e t o t a l w a t e r a n d J M P o r t a l

o r g a m c C a n d N W e a r e g r a t e f u l t o D D a u t e l ,M G o r a u , A L e g r o s a n d C N e t t e r f o r t y p i n ga n d d l u s t r a t m n s T h e f ie ld e x p e n s e s w e r e s u p -p o r t ed b y P I R P S E V P r o g r a m m e I nt er d ls c~ -p h n m r e d e R e c h e r c h e s u r l a P r ~ w s m n e t l aS u r v e i l la n c e d e s ] ~ r u p tm n s Vo l c a m q u e s C e n t r eN a t m n a l d e l a R e c h e r c h e S c m n t f f ~ q u e )

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