1. Northwest Africa 5738 An 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
75th Meteoritical Society Meeting, Cairns, 14 August 2012

2. 22 stones found in 2009, total 2.2 kg
NWA 5738
22 stones found in 2009, total 2.2 kg

3. backscattered electron image
NWA 5738
backscattered electron image
ARTIFACT
0.5 mm

4. PYROXENE COMPOSITIONS

5. Mayne et al. (2009) NWA 5738 primary plag.
NWA 4523 (3 different clasts)
cumulates
NWA 5738 primary plag.

7. Impact-melt vein
NWA5738 “Dark” JEOL mosaic

8. NWA5738 ‘dark’ JEOL mosaic: 5738b001-gammaed.bmp

9. Analysis of bulk NWA 5738 by CO2 laser-fluorination at KOPRI (avg
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‰
brach
NWA 5738
Base diagrams: Mittlefehldt et al. (2008)

10. NWA 5738
Base diagram: Scott et al. (2009)

11. NWA 5738
10 separate grains
Base diagram: Compositions of metals from HED impact-melt breccias (within howardites; Lorentz et al., 2007)

12. Ni peak

13. Sc peak

15. Earth’s Continental Crust
as represented by shale composites

18. Nuevo Laredo
trend
NWA 5738
Stannern
trend

19. Stannern
trend
Nuevo Laredo

20. Stannern
trend
Nuevo L. trend

21. Barrat et al. (2011)
BSE images of NWA 049

22. SdM, Treiman et al. (2004)

23. SECONDARY MINERAL ASSEMBLAGES IN EUCRITES

24. Fe–olivines Fe–olivines C a – p l a g p y r o x e n e
NWA57382B-220x-plag-Fa trains.bmp
p y r o x e n e

25. C a – p l a g p y r o x e n e Fe–olivines
NWA57382B-1300x-fault displacing both plag vein and exsolution lamellae
p y r o x e n e
Fe–olivines

26. C a – p l a g
C a – p l a g
chromite
p y r o x e n e

27. C a – p l a g
p y r o x e n e
F e – o l i v i n e

28. F e – o l i v i n e p y r o x e n e C a – p l a g
NWA57382B-400x-trains of mainly Fa with lesser plag and one tiny probed cm-located shortly W of the trains discovery site
C a – p l a g
p r i m a r y p l a g

29. cf. Barrat et al. (2011)
PLAGIOCLASE
COMPOSITIONS
NWA 5738

30. C a – p l a g + s i l i c a
C a – p l a g
p y r o x e n e

31. C a – p l a g + s i l i c a F e S p y r o x e n e
NWA5738-2B - alteration patches of An plus silica within px - large bright grain is FeS .bmp
p y r o x e n e

32. p y r o x e n e
F a – r i c h o l i v i n e s s
chromite

33. z i r c o n C a – p l a g ? p y r o x e n e
[NWA57382B-3000x-zircon in plag-Fa trains area.bmp]
p y r o x e n e

34. SECONDARY MINERAL ASSEMBLAGES IN EUCRITES

35. C O N C L U S I O N S NWA 5738 is an extraordinary eucrite
Its oxygen isotopes have a low, NWA-1240-like Δ17O
Its 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 trend
NWA 5738 shows extensive development of secondary mineralogy:
Unprecedented combination of Fe-olivine, Ca-plagioclase (etc.)
with silica
in 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.
Pl2 and Fa trains seem to be confined to px; suggests deposition from fluid, where the deposition process was sensitive to the substrate on which deposition occurred.