Proposed one-bar phase equilibrium experiments, designed to determine the compositions of the nakhlites' parental magmas, are in progress. Proposed field studies on Earth, designed to find occurrences of rocks like the nakhlites, were extraordinarily successful. Other work supported in the past year included: attendance at the 1986 national meeting of the Geological Society of America; attendance at the 18th Lunar and Planetary Science Conference; completion and publication of a study of core formation in the SNC parent body; initiation of a study of the flux of SNC meteorites onto the Earth; and initiation of petrologic study of the Angra dos Reis achondrite

Treiman, Allan H.

English

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( N A S A - C R -  181 133)  BETEORITXC E A S A L X S :  ?HE N37-26713 
BETES, A b C  ECli.LVPEENNTS C N  EAfiTk €inal 
IEchnica l  ReFcrt (Boston U n i v . )  1 0  p Unclas 
A v a i l :  N l I S  BC A01,"F A01 CSCL 0.38 G3/90 00838Cb 
b A K H L I T E S ,  T H E 1 6  € A B E N T A L  t J A G t . A S ,  CCOLILJG 
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Contents 
1 SUMMARY 
Furiding for N A S , i  grant YL4G 9-168, titlcd “2lctcoritic Ikisalts: the Yakhlites, their Parental Ma- 
mas, (’ooling Rates, arid Equivalents oii Earth,” receiietl at Boston University on July l ,  1986. 
One y e a r  of research has been cornplct c d .  I’ropowd one-bar phase equilibrium experiments, de- 
signed to dctermine the compositions of the rtakhlites’ parc>rttal magmas, are in progress. Proposed 
field studies on Earth, designed t o  find o(ciirrances of rock5 like the nakhlites, %ere extraordinarily 
su cc  essfu 1. 
Other  work supported in the past jear h j  ttii.; NASA grant includes: dttendance at the 1986 
national meeting of t he Ccological Socictj of iritc.rica; attciidaricc at t tic 18th Liinar and Planetary 
Science Conference; completion and pu1)licat i o n  of  a study of torch foriliation i n  the SNC parent 
body; iriitiatiori of a study o f  the flux of 5\(’ irlet(writcs onto the Ear1 h ;  arid initiation of petrologic 
study of the Arigra dos Rcis achondrite. 
2 WORK COMPLETED 
2.1 One-Bar Experiments 
E.iprrirric.rita1 stttdic,s were propowd to tcbst the trjpot hesis of Treirnan 11; that  the nakhlites formed 
fror i i  ult rdhctsic riiagiria~. a n d  to estimate the rd tes  a t  M I i i c  t i  t tiose tiragmas coo1c.d. Much of the 
past j car tia5 hceii spviit i n  final a swrnb l~  and (alihrat ion  of t hci one-bar furriace fa( ility. I now have 
a full! o p  rational \ r r t ical  muffle tube furnace ( Ik l tcch  1)7‘-RI-\“T-OS-C), equipped for controlled 
atiiio\plic~rc~s and  i i i ~ ~ ~ ~ i ~ r t ~ r i i ~ ~ n t  of ox3gcn fugacity. The terirperature tor i t  roller allows for linear 
heating and cooling. ‘I’r~nipc~rature is mcasurvd M i t  t i  a type-S t tic~rrnocouplr calibrated against the 
melting point of gold and a secondary $tar idad t trt.rrnoc o~ ip lc  t ra( cable t o  the National Bureau 
of St artcldrd~. Oxygen fuga( i t  y is rriea5rirc4 uit 11 an y t  t r ia -s ta I ) i l i~~d Airconia electrode, calibrated 
accurate t,o r0.05 log units f(O2) a t  the iron-wiistite h f f o r .  
Equilibrium crystallization studies were i r i i t i a t d  to  dctcrrriine the cornposition of Nakhla’s 
intercumulus niagma, the best available sample of the rnagriia from uhich the nakhlites formed i l l .  
Starting rnaterials are synthetic powders corrcsporiding t o  calculat rd possible parent magmas. The  
powders are melted to  glass beads on  platinurn loops. Experiments SO far are syntheses, using these 
glass beads, at the temperatures of interest arid oxygen fugacities slightly above the iron-wiistite 
buffer. 1,iquidus and cotectic temperatilros M i l l  be confirnitd by reversal experiments. A table of  
experimental rc~sults is included here as IJ’I’b;5DIX A. 
k ’ a l i s e  Nahhla’s intercumulus mrigiiict \ \as sat iiratcd i n  augite and olivine, phase equilibriurn 
expcrirrierits seek to  determine thc augit c , - o l i \  i r i r  cotectic (i.e. melt compositions and tempcrat lire’s 
u here augite, oli\ ine and melt arc’ stal)lc t o g c b t  her). 1,iquidiis temperatures for the intercuriiiilus 
magma corriposit i o n \  are  rimr l3OO‘’(‘.  ‘I’tic, t ) c , t - h i i o w r i  to date. t h a t  of composition C [ I  , is 
12821 lo*(’. Olivine is the liquidiis phaw for compositions 13, C’ and D (APPENDIX A), and 
presumably for coinposition A which is richest i n  oli\ine corriponent. This implies that  t tic. aiigite- 
olivine cotectic is at more augite-rich corripoit ions  t hari  I). The augite-olivine cotectic is near 
126O”C‘, based on results from compositions C arid 11. 
Compositions A t Iirough 1) here  calculated (by n i i l ~ s  balance) for 2040% interciirnuliis magma; 
D corresponds to the most intercumulus magma 11 j. f3rcau5e the cotect ic is a t  cornposit ions more 
aiigite-rich than D, Y i l k h l a  must have contained rriore than 40% trapped melt among the cumulus 
augite and olivines. This percentage is greater than originally siiggrsted, and implies t h a t  the 
cumulus grains in  Nahhla compacted little a f t e r  settling. In retrospect, this swms reasonable. 
There would have been little gravitational force for (or l ipac t ion ,  because the densities of the grains 
and the melt m e r e  similar. Compaction would be further hindered by post-curriul~is grain growth, 
which is docurneritcid in the nakhlites [1,2]. 
No oxide minerals were observed in the low-teniperature ( 1  125°C’) runs, siiggesting t h a t  oxygen 
fiigacity in the experiments is lower than t h a t  expeririiced by the nahhlites. The  intrinsic oxygen 
fugacity d a t a  of i3j are i n  accord with this limit,. 
2.2 
The nakhlites are  unusual among igneous rocks twcauw t h e y  are  cumulates with fine-grained, 
quench-textured material (mesostasis) among the settled grains. To understand how the nakhlites 
furiiied. 1 looked fur Earth rocks of similar minc~alogy a n d  text  l ire as analogs t o  the meteorites. 
Rased on literature descriptions, I proposed field study near Tirnrnins (Ontario) t o  examine cumu- 
late rocks in thick flows and shallow sills. The  study was successful beyond expectations. Some of 
the  cumulate rocks are nc,arlj identical, niineralogically and texturally, to the nakhlite and Chas- 
signy meteorites. I f  the Ontario rocks had  not been metamorphosed, it uould have been dificult t o  
tell them from the rnrtcwrites. Preliminary results of the field study a re  given in 141 (see A P P E N D I X  
B for this paper and two related abstracts). 
Field studies %(’re conducted during the first three weeks of August, 1986 in northern Ontario. 
Base camp for field work w a s  Kettle Lakes Provincial Park,  Ontario, where I carriped. Tht, weather 
mas good, and only one rainstorm (10 cm in one day) hindered study. Insect life mas n o t  a problem. 
The  first rock unit studied wa5 the Dundonald Sill of Dundonald and Clergue ‘I’ounships, 
Ontario 151. It is a 300+ meter thick body of basaltic composition, differentiated frorri  grariophjric 
gabbro at its t op  t o  pryoxenite and dunite a t  its base. The  sill is cut by fault. and has experienced 
grwnschist facies metamorphism. Some samples o f  dunite and pyroxenite, poasibly frorn t h c  sill. are 
tc.xturally similar to the Chassigny and Lafayette metteorites and are  figured i n  1 4 1 .  The meteorite 
analogs occur in a fau l t  block abutting gabbro and pyroxenite of the sill, but the sill’s pyroxerrite 
is significantly coarser-grained than the faul t  block’s pyroxenite. T h e  rocks of t h e  fault block not 
be from the  sill, but  possibly from a ‘koniatiite’ flow intruded by the sill. 
The How 
is wedge-shaped, 30-125 meters thick, and is differentiated to  gabbro. curnulat e pyroxcnite, and 
Terrestrial Analogs to the Nakhlites and Chassigny 
The second rock unit studied w a s  Thee's flow in  M u n r o  Township, Ontario IS]. 
3 
ciirnulat E peridotite. ‘I’hc gcologic structure near Thw’s flou is iirrarti1)iguous. Elcpo5iirc. of t h e  fjow 
is repeated b y  a fault, but t h e  fjow is not disriipted o r  folded. The whole region experienced mild 
nictarriorphisrn. but n o  pcnetrat i \  e deforriiat ion.  
T h e  pj  roxenites of ‘Fheo‘s flow arc text u ra l l j  ideritical to  the Nakhla and Governador Valadares 
metcwrit m, except for the effects of met amorphism. Photomicrographs of the rocks and the mete- 
orites are gi\en in 141. T h e  rneteoritts and these Earth arialogs are all augite-rich cumulates w i t h  
sonic’ c uniulus olivine, have poikilitic olivine grains among the augite, and h a v e  quench-textured 
rnrsu.;tases among their cumulus grains. Grain sizes in the mesostases are comparable, suggesting 
similar cooling rates and therefore similar geologic settings. 
I t  wcnis fair t o  con( lude that  Nakhla and Goternador Valadares formed in th ick  flows similar 
to ‘J’heo’s flow. If  one accepts tha t  the  nakhlit,es are from Mars, tha t  planet must have had thick 
flows of basaltic (or ultrabasic) lava which differentiated in situ. 
2.3 Petrography and Mineral Chemistry 
Petrography and niinrral chemistry have served as tools i n  experimentiil and field studies (above). 
Petrofabric studies i n  the preceeding propc)saI were  d ~ l a y e d  because the Depart rrient’s uni\ ersal 
stage has vanished. Dr. . I .  L. Rerkley has kindly loaned me a replacement. 
,% noteworthy pf ‘rographic observation is that  augites in the nakhlites (particularly GoLernador 
Valadares) contain magmatic inclusions, composed of glass, magnetite, olivine(?) and vapor bub- 
bles. The  vapor bubbles are of interest as possible hosts for nobltk gasses in the nakhlites 171. I a m  
in correspondence with Dr. T. Swindle, noble gas specialist at the University of Arizona, about  
the inclusions. 
2.4 Flux of SNC Meteorites 
The f lux of SNC meteorites onto the  Earth is important i r t  understanding the mechanism of their 
ejection from hlars, and t h e  dynamics of their transit to Earth.  Heccmt studies have assumed a 
cons tan t  flux of S;NC rneteorites for millions of years \8,9], but without control o n  possible time 
depend(~rice. Meteorite falls, finds, and Antarctic finds represent sarriples of the meteorite flux to 
Eart h in  different time periods, and the  proportios of SNC meteorites in these populations indicates 
t h a t  the f lux of SNC meteorites has been constant, a t  least over the last hundred thousand years. 
Obserced meteorite falls represent a sample of the meteorite flux w i t h i n  the last 200 years. 
Among the 959 recorded meteorite falls 1101, four are SNCs for a flux proportion of 0.42%. Of 
basaltic rrieteorites, 7.7% are  SNCs. Although large and metallic meteorites are probably over- 
represented, the proportions of falls may be close to  the real proportions of meteorites falling onto 
the Earth today. 
Among non-Antarctic meteorite finds, the best indicator o f  SNC flux is t h e  proportion of SNC 
meteorites to  basaltic rrieteorites of siniilar lithology, the IlED sujte. Stony rrieteorites are  under- 
4 
reprcwrrt(d twc iiiise i ron  meteorites arc. distirrc t i k e  arid rc.sistant to  weathering. Ijasaltic rneteoritw 
may be f u r l  tier 1iridc.r-rc.prc.sented becuaw they look so niiich like terrestrial basalts. Aniong the 
12 finds o f  basaltic ac hondriles, 2 are SNC rrieteoritcls, for a proportion of 4.8%). 
4moiig t h c l  Antarctic meteorites the best indicator of SNC flux is also the proportion of SNC 
mc.tcorites to  1IKD basaltic achondrites. 24any Antarctic nic%teoritt.s are paired and thus the nuniber 
of catalogcd nietrorites does not represent the number of falls. Approximately 1100 separate stony 
tnc,tcoritc falls rriay be represented [ 11,121 in the C.S. collections, possibly fewer because of the 
difficulty i n  pairing ordinary chondrites. The basaltic rneteorites have been extcnsively studied and 
the -58 cataloged samples came from 32 falls. Of these, 2 are SNC meteorites for a fraction of 6.25%. 
The prcwrit -day proportion of SNC mcteorites to FIED meteorites, 7.7%, is (wentially identical 
to the SNC‘, 11k:I)  proportions among non-Antarctic finds (4.8%) and Antarctic finds (6.25%). 
Taking the proporiinn of HED meteorites t o  stony meteorites from the fall data ,  one may infer t h a t  
0.4of s t o n y  rnrtcwrites (within the time sampled) have bcrn SNCs. 
Based on this aswvnent  of the  historical record, the f lux  of SNC meteorites has been constant 
for the last few hundred thousand years, the akerage age o f  the Antarctic meteorites. However, one 
cannot infer wi th  certainty that  the flux has bwn  con\tant for eken a few million years. 
2.5 Angra dos Reis 
The .2ngra dos R e i s  rnrt eorit c s  is a ~iniqiie calt iurti-rich ac horrtlrite, conipowd almost entirely of 
faqsaite pyroxene (,41-Ti aiigite). Dr.  John H .  Joncs arrd 1 ha\e bcgun a rc-evaluation of the 
origin of Angra dos Reis. elevcn Sears after the l l ) O R A l ~ l , t ~ ~ S ’  studies :13].  Xly work will focus on 
petrology, and his work (included in an irrdepcnc’(~nt grant proposal) will focus on geochemistry. 
Already complete is an abstract on tcxxtural relatioris i n  .4ngra dos Reis (see APPENDlX B). 
Textures of Angra dos Reis siiggest tha t  it i.; a quick13 coolod or qiienched rnagrna with amoeboid 
phenocrysts. This interpretation is at Lariarice with t h a t  of 1133, and suggests t ha t  geochemical 
modelling of the meteorite ntii5t be revised. 
I n  progress is a st udy of crystallization and phasc equilibria of Angra dos Reis. In general, its 
crystdllizatiori is consistent with the phase equilibria for Fe-free fassaite pj  roxene [ 141, modified for 
the effects of added iron. 
2.6 Conference Attendance 
T h i s  grant supported attendance a t  two conferences: the 98th annual meeting of the Geological 
Society of Arrierica (November 10-13, 1986; San Antonio, T X ) ,  and the Lunar  and Planetary Science 
Conference (March 16-20, 1987; Houston. T X ) .  Funds originally budgeted for attending the meeting 
of the Xleteoritical Society were used to partially defray costs to the Geological Society meeting. I 
could not attend the Meteoritical Society conference because of illness. 
5 
My primary int,crest at; the c.onferc.rice o f  t Irc (;c.ological Society of America was a scwion t itled 
“Layered hlafic Intrusions arid Rrlat.ed Topics.’‘ The sossion feat,ured several talks useful in the 
interpretatlion of  the riakhlit.es as cilrriu1at.e rocks; of part,iciilar use was the talk by Dr. C. Cha lokwu ,  
w h o  has been studyirig niet.hods o f  retrieving riiitgr~ia cortiposit ions from igneous rocks. 
A t  the Eighteenth Lunar and Planet.ary Scirrice Coiiference, I presented a paper on the geolog- 
ical origins of the nakhlite arid Chassigny metoorites (s(w APPENDIX B), and at.tended sessions 
on Martian geology, basaltic achondrit,cs, and urcilites, arnnng others. Of particular value were 
informal conversatons about, noble gasses in the r i akh l i t  es, Angra dos Reis, arid the geomorphology 
of Martian lava flows. 
3 REFERENCES 
j I ]  Trvinian A . H .  (1'386) The parent a1 magina of t h e  N a k h l a  achondrite: Ultrabasic volc anisrn on 
t h r  shcrgottite parent bod). Ceochitn. Cosmochim. Acta.-5Q, 1061-1070. see APPENDIX B. 
121 13erhley J.L., Keil K .  and Prinz M .  (1980) Comparative petrology and origin of Governador 
Valadares and other nakhlites. Proc. Lunar Planet. Sci. Conf. 1 I j h ,  1089-1102. 
, 3 ]  Delano J .W.  and Arculus R.J. (1980) Nakhla: Oxidation state and other constraints. (abstract)  
141 'I'reiit)an .\.H. (1988?) 
Lunar Sti.-X_l, 219-221. The 1,uriar and Planetary Inst,itute, Houston. 
Geology of thc nakhlit~e and Cha5signy meteorites: Equivalents on 
Earth and implications for hlars. for suhinission to Proc. 19th Lunar Plan_et..Sci. Conf. see 
A P P E N D I X  B. 
151 Naldrett A.J.  and >lason G.D. (1968) Corrt rasting Archean ultramafic igncous bodies in Dun- 
donald and Clcrgue tohiiships, Ontario. Can. Jour. Earth Sci, 5, 1 1  1-143. 
:6] Arndt N . T .  ( 1 ~ 7 )  T h i c k ,  layered ~"'rid"titc-gilbbro la\a flows in Munro Township, Ontario. 
Can. Jour. Earth S( i. 11, 2620-2637. 
,7] Swindle T.D.. Garriwii I ) . ,  Iloherihc~rg ('.V., and Olingrr C.7'. (1987) X e n o n  and argon in 
Yakhla and 1,afajettr: E\ideirce for riliiltiple "24artiann conrponrr~ts (abstract). Lunar Planet. 
Sci. X c l I l ,  98.1-985. 'l'hc Lunar arid l'liiirct a r y  Instit U t e ,  llouston. 
'8; U'etherill G . W .  (1984) Orbital e\oliitiorr o f  iirtpac t ejecta from i\lars. Slctcwritics 19, 1-13. 
[9] Vickery A . M .  and h l ~ l o 5 h  l l . J .  (1987)  'I'Jic. large crater origin of SNC Ineteorites. Science, in 
press. 
/ I O ]  Graham A.L., Bevan A.W.Jt .  and Ilutchison R. (1985) Catalog of Meteorit,es, with Special 
Reference to those Ilepr(wnted i n  the Collection of the British Museum (Natural History, 
Fourth Edition. University of Arizona F'w+ Tucson A%. 
11 I ]  Gooding J.L.  ed. (1986) Index of Classified Lleteorites from the 1976-1985 Antarctic Collec- 
tions. Antarctic Meteorite Newsletter Y:4.  Johnson Space Center, Houston. 
, 1  21 Ant arctic Meteorite Newsletter (1987) vol.10, # l .  Johnson Space Center, Houston. 
: 1 3  
1 1  
Prinz M., Keil ti., Hlava P.F., Rerkley J.L., Gomes C.B. and Curve110 W.S. (1977) Studies of 
Urazilian meteorites, 111. Origin and Ilistory of the Angra dos Reis achondrite. Earth Planet. 
Sci. Lett. 35, 317-330. 
Stolper E. (1982) Crystallization sequences of Ca-Al-rich inclusions from Allende: An experi- 
mental study. Geochim. Cosmochim. .Acta. 45, 2159-2180. 
7 
4 APPENDIX A: RESULTS OF EXPERIMENTS 
Run # Conip. 
B1J-10 
BU-11 
BU-20 
BU-14 
BU-17 
BU-16 
BU-15 
1317- 13 
1311-29 
1311-27 
ljl .-28 
B 
C 
C 
C 
C 
C 
C 
C 
D 
I1 
r) 
rr ( o c )  
1291 
1291 
I273 
I267 
124'3 
1225 
1155 
I I25 
1268 
1257 
12.50 
I'h ascs 
gl 
gl t 01 
gl t ol 
gl t 01 i au 
gl t 01 t au 
gl + 01 i all t PI(?) I op 
01 t au t p1 
gl i 01 
gl + 01 i au 
gl + nl + au i np 
Rtisii l ts  o f  ~)hase-cqiiilibriiim experiments on the origin o f  the naklilites. Compositions are those 
of  3 ' ,  aiid rc>prcwnt a range of possit)lr intercumulus riiagrrias i n  the Yaktila meteorite. Oxygen 
firgac itios f o r  cornpositions I3 and C are approxirnatelj 0.25 log iiriits aboke the iron-wiistite buffer; 
f o r  composition D, oxjgeri fiigacity is 1 log u n i t  above iroi l - \ s  iistitc,. .Il,l)re\iations for phases 
present are: gl, glass; 0 1 ,  olivine; ail, augite; pl, plagioclase; and op. opaques. 
8 
"* 
5 APPENDIX B: PUBLICATIONS AND PREPRINTS 
Trviman A.H. ,  Jones J . H .  and Drake M . J .  (1987) Core formation in the  Shergottite Parent Body 
and cornparison R i t h  t he  Earth.  Proc. 17th Lunar Planet. Sci. Conf. J .  Geophys. Res. 92 
Suppl., E627-E632. 
Trriman A.H. (1987) Geology of the nakhlite meteorites: Cumulate rocks from flows and shallow 
intrusions (abstract). Lunar Plane!,. Sci.(VlIl, 1022-1023. Liinar and Planetary Institute, 
Houston. 
'I'rcSiiJian A . H .  (1987) Geology of the nakhlite and Chassignq meteorites (abstract). Meteoritics 22, 
i n  press. 
'l'rcirnan A . H .  (1988?) Geology of t he  nakhlitc and <:liassigny niet eorites: Equivalents on Earth 
and intplications for Rlars. Preprint for submission to  h o c .  19th Lrtnar Plgnet. Sci. Conf. 
'I'rc.irrian .4.1J. (1988?) The  textures and origin of Artgra dos Rc>is: Still adorable after all these 
Scars? (abstract) Preprint for subniission to Lunar Planet. Sci. XIX. 
9 


Meteoritic basalts: The nakhlites, their parental magmas, cooling rates, and equivalents on Earth

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