Northwest Africa 5738 An Extraordinarily Evolved Eucrite P

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 75 th Meteoritical Society Meeting, Cairns, 14 August 2012

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

NWA 5738 backscattered electron image T 0. 5 mm AC F I T AR

PYROXENE COMPOSITIONS

Mayne et al. (2009) cum ulat es NWA 4523 (3 different clasts) NWA 5738 primary plag.

Analysis of bulk NWA 5738 by CO 2 laserfluorination at KOPRI (avg. of 2 similar analyses): δ 18 O = 3. 589‰, δ 17 O = 1. 617‰ Δ 17 O = ‒ 0. 271‰ ch NWA 5738 Base diagrams: Mittlefehldt et al. (2008) bra

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

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

Earth’s Continental Crust as represented by shale composites

Nuevo Laredo trend NWA 5738 Stannern trend

Nuevo Laredo trend Stannern trend

Stannern trend Nuevo L. trend

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

SECONDARY MINERAL ASSEMBLAGES IN EUCRITES

pyroxene Ca–p lag Fe–olivines

C a – p la g pyroxene es in liv –o Fe

Ca– plag C a – p la g chromite pyroxene

Ca –p la g pyroxene F e–o l e n i iv

F e – o v i l in e pyroxene Ca– plag ag l p ry a m pri

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

Ca–p l a g + s i l i c a Ca–plag pyroxene

Ca– p l a g + s i l i c a Fe. S pyroxene

pyroxene F c te i m o r h a – r ic h o l i v i n e s s

zir con Ca–p p y r o x e n e lag?

SECONDARY MINERAL ASSEMBLAGES IN EUCRITES

CONCLUSIONS NWA 5738 is an extraordinary eucrite Its oxygen isotopes have a low, NWA-1240 -like Δ 17 O Its primary plagioclase is extremely sodic (average An 74) 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.