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75th Meteoritical Society Meeting, Cairns, 14 August 2012

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.

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75th Meteoritical Society Meeting, Cairns, 14 August 2012

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

  3. NWA 5738 backscattered electron image 0.5 mm ARTIFACT

  4. PYROXENE COMPOSITIONS

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

  6. 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 NWA5738 Base diagrams: Mittlefehldt et al. (2008)

  7. NWA5738 Base diagram: Scott et al. (2009)

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

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

  10. Nuevo Laredo trend NWA 5738 Stannern trend

  11. Nuevo Laredo trend Stannern trend

  12. Stannern trend Nuevo L. trend

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

  14. SECONDARYMINERALASSEMBLAGESINEUCRITES

  15. Fe–olivines Fe–olivines C a – p l a g p y r o x e n e

  16. C a – p l a g p y r o x e n e Fe–olivines

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

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

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

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

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

  22. Ca–p l a g + s i l i c a F e S p y r o x e n e

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

  24. z i r c o n C a – p l a g ? p y r o x e n e

  25. SECONDARYMINERALASSEMBLAGESINEUCRITES

  26. 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.

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