75th meteoritical society meeting, cairns, 14 august 2012
DESCRIPTION
Northwest Africa 5738 An Extraordinarily Evolved Eucrite P. H. Warren 1 , J. Isa 1 , N. Gessler 2 , I. Ahn 3 and B-G. Choi 4 1, UCLA 2, Duke University 3, Korea Polar Research Inst. 4, Seoul National University. - PowerPoint PPT PresentationTRANSCRIPT
75th Meteoritical Society Meeting, Cairns, 14 August 2012
Northwest Africa 5738An Extraordinarily Evolved
Eucrite
P. H. Warren1, J. Isa1, N. Gessler2, I. Ahn3 and B-G. Choi4
1, UCLA 2, Duke University 3, Korea Polar Research Inst. 4, Seoul National University
NWA 573822 stones found in 2009, total 2.2 kg
ARTIFACT0.5 mm
NWA 5738
backscattered electron image
PYROXENE COMPOSITIONS
0 10 20 30 40 50 60 70 80 90 100
50
40
30
20
10
En Fs
Di HdNWA 5738
Cumulate eucrites Moama Serra de Magé Nagaria Moore County Pomozdino
Noncumulate eucrites Y-791195 Juvinas Haraiya Nuevo Laredo
NLHJY
PMCN
SMM
Mayne et al. (2009)cu
mul
ates
NWA 4523 (3 different clasts)
NWA 5738 primary plag.
20
30
40
50
60
70
80
90
100
110
0 1 2 3 4 5 6bulk Na (mg/g)
bulk
Mg
(mg/
g) noncumulate cumulate
NWA 5738
Ibitira
E U C R I T E S
brach
NWA 5738
Base diagrams: Mittlefehldt et al. (2008)
Analysis of bulk NWA 5738 by CO2 laser-fluorination at KOPRI (avg. of 2 similar analyses):
δ18O = 3.589‰, δ17O = 1.617‰Δ17O = ‒0.271‰
NWA 5738
Base diagram: Scott et al. (2009)
Base diagram: Compositions of metals from HED impact-melt breccias (within howardites; Lorentz et al., 2007)
NWA 573810 separate grains
166000
168000
170000
172000
174000
176000
178000
795 800 805 810 815 820 825energy (keV)
coun
ts
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
870 875 880 885 890 895 900 905energy (keV)
coun
ts
10
100
Sr Ba La Ce Nd Sm Eu Tb Dy Ho Yb Lu Hf Ta Th U
REE
sam
ple/
CI c
hond
rites
(wt.
ratio
)
30NWA 5738
BouvanteStannern Trend
Juvinas'Main Group'
(literature averages)
warm-desert alteration
Earth’s Continental Crustas represented by shale composites
10
100
Sr Ba La Ce Nd Sm Eu Tb Dy Ho Yb Lu Hf Ta Th U
REE
sam
ple/
CI c
hond
rites
(wt.
ratio
)
30NWA 5738
BouvanteStannern Trend
Juvinas'Main Group'
(literature averages)
warm-desert alteration
18
22
26
30
34
38
0 1 2 3 4 5bulk Sm (µg/g)
bulk
Sc
(µg/
g)
noncumulate cumulate
Kapoeta clast F4
NWA5738
E U C R I T E S
Nuevo Laredo trend
Stannerntrend
NWA 5738
18
22
26
30
34
38
0 1 2 3 4bulk Yb (µg/g)
bulk
Sc
(µg/
g)
noncumulate cumulate
Kapoeta clast F4
NWA5738
E U C R I T E S
Stannerntrend
Nuevo Laredo trend
0.0
1.0
2.0
3.0
4.0
5.0
30 40 50 60 70bulk Mg/(Mg+Fe), mol%
bulk
Sm
, µg/
g noncumulate cumulate
Kapoeta clast F4NWA5738 E U C R I T E S
Nuevo L. trend
Stannerntrend
Barrat et al. (2011)BSE images of NWA 049
SECONDARY MINERAL ASSEMBLAGES IN EUCRITESThermalmetamorphism? Fe-px Fe-ol Ca-plag Silica Chromite Troilite Zircon Apatite references
NWA 1000 Ext. low Yes Yes - - - - - - Warren
NWA 2061 Ext. low Yes Yes Yes - - - - - Barrat
NWA 5073 Ext. low Yes Yes Yes - Yes Yes - Yes Roszjar
Y-75011 Ext. low Yes Yes Yes - - - - - Barrat
Y-82202 Ext. low Yes Yes Yes - - - - - Barrat
NWA 049 Low Yes Yes Yes - - - - - Barrat
Pasamonte Low Yes Yes - - - - - - McCallum, Herd, Barrat
NWA 5738 Normal - Yes Yes Yes Yes Yes Yes? - THIS WORK
Sioux County Normal* Yes Yes Yes Yes - - - - Barrat*
Serra de Magé High (cumulate) - - - Yes - - - - Treiman
* "Despite a careful search, Fe enrichments along cracks in pyroxenes from equilibrated eucrites have not yet been observed ." Polymict breccia Sioux County is the one exception .
p y r o x e n eC
a –
p l a
g
Fe–olivines
Fe–olivines
p y r o x e n e
C a – p l a g
Fe–olivines
p y r o x e n eC a – p l a g
chromite
C a – p l a g
p y r o x e n eC a – p l a g
F e – o l i v i n e
p y r o x e n e
p r i m a r y p l a g
C a – p l a g
F e – o l i v i n
e
0 10 20 30 40 50 60 70 80 90 100
50
40
Ab An
primary
secondary
Or Or
20
10
30
NWA 5738
PLAGIOCLASECOMPOSITIONS
cf. Barrat et al. (2011)
C a – p l a g + s i l i c a
p y r o x e n e
C a – p l a g
p y r o x e n e
F e S
C a – p l a g + s i l i c a
p y r o x e n e
F a – r i c h o
l i v
i n e s s
chromite
p y r o x e n e
C a – p l a g ?
z i r c o n
SECONDARY MINERAL ASSEMBLAGES IN EUCRITESThermalmetamorphism? Fe-px Fe-ol Ca-plag Silica Chromite Troilite Zircon Apatite references
NWA 1000 Ext. low Yes Yes - - - - - - Warren
NWA 2061 Ext. low Yes Yes Yes - - - - - Barrat
NWA 5073 Ext. low Yes Yes Yes - Yes Yes - Yes Roszjar
Y-75011 Ext. low Yes Yes Yes - - - - - Barrat
Y-82202 Ext. low Yes Yes Yes - - - - - Barrat
NWA 049 Low Yes Yes Yes - - - - - Barrat
Pasamonte Low Yes Yes - - - - - - McCallum, Herd, Barrat
NWA 5738 Normal - Yes Yes Yes Yes Yes Yes? - THIS WORK
Sioux County Normal* Yes Yes Yes Yes - - - - Barrat*
Serra de Magé High (cumulate) - - - Yes - - - - Treiman
* "Despite a careful search, Fe enrichments along cracks in pyroxenes from equilibrated eucrites have not yet been observed ." Polymict breccia Sioux County is the one exception .
C O N C L U S I O N SNWA 5738 is an extraordinary eucriteIts oxygen isotopes have a low, NWA-1240-like Δ17OIts primary plagioclase is extremely sodic (average An74)
The bulk composition is commensurately Na-rich also exceptionally rich in incompatible trace elements despite moderate Sc and mg ratio
... extends the Stannern trendNWA 5738 shows extensive development of secondary mineralogy: Unprecedented combination of Fe-olivine, Ca-plagioclase (etc.)
with silicain a normally equilibrated eucrite
Secondary veining probably developed when fluid (aqueous?) percolated through the rock after it had undergone some brecciation and cooling. Precipitation of new phases occurred preferentially in cracks in pyroxene, possibly b/c pyroxene provided a more reactive substrate.