Lee, M.R.

Lindgren, P.

Smith, C.L.

Sofe, M.R.

English

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Sofe, M.R., Lee, M.R., Lindgren, P., and Smith, C.L. (2014) Three phases 
of carbonate minerals and two degrees of alteration in the Nogoya CM2 
carbonaceous chondrite. In: 77th Annual Meeting of the Meteoritical 
Society, 8-13 September 2014, Casablanca, Morocco. 
 
 
Copyright © 2014 The Authors 
  
 
 
http://eprints.gla.ac.uk/97474/  
 
 
 
 
 
Deposited on:  25 September 2014 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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THREE PHASES OF CARBONATE MINERALS AND 
TWO DEGREES OF ALTERATION IN THE NOGOYA 
CM2 CARBONACEOUS CHONDRITE
M.R. Sofe1, M.R. Lee2, P. Lindgren2 & C.L. Smith3. 1AL Gabal 
Al Gharbi University, Libya, E-mail: mahmood.sofe@gmail.com
2
University of Glasgow, G12 8QQ, UK. 3Natural History Muse-
um, London SW7 5BD, UK
      Introduction: The Nogoya CM carbonaceous chondrite has 
been described as highly altered by [1], classified as a CM2.2 by 
[2], and found to be more highly altered than Mighei (CM2.3) yet
less altered than Cold Bokkeveld (CM2.2) [3]. The present study 
indicates that Nogoya can in fact be divided into two contrasting
lithologies that differ in degree of alteration and carbonate miner-
alogy; one is a CM2.2 and the other a CM2.3. Here we have 
sought to understand the alteration conditions that produced the 
two Nogoya lithologies.
      Methods: BSE imaging and EDX-ray analyses of a polished
and carbon coated thin section of Nogoya were undertaken in a 
field emission Zeiss Sigma SEM operated at 20 kV. TEM anal-
yses were performed on three FIB liftouts of dolomite and 
intergrown minerals as well as Mg-rich serpentine after calcite. 
Diffraction contrast images and diffraction patterns were acquired 
using a FEI T20 TEM operated at 20 kV. Raman spectroscopy 
and EPMA were also used in this study for mineral identification 
and quantitative chemical analysis respectively.
      Results and discussion: Petrographic observations indicate 
that in the more highly altered of the two lithologies the majority 
of Mg-rich olivine grains have been replaced by serpentine, and 
Fe-Ni metal is near absent from mafic silicates. Therefore, this 
lithology has been classified as CM2.2. The less highly altered 
lithology is a breccia, and texturally analogous to the matrix of 
Mighei. Most of Mg-rich olivine grains are well preserved. In 
some cases their margins are etched, and have been replaced by 
calcite or phyllosilicates. The abundance of Fe-Ni metal in this 
lithology is less than 0.2 vol. %, although rare intact metal grains 
were observed inside olivine grains. Thus, these observations
suggest that the less altered Nogoya lithology is a CM2.3. The 
matrix of the CM2.3 lithology has higher concentrations of Mg 
than the CM2.2 region, which is consistent with the fact that the 
matrix of CM chondrites becomes enriched in Mg with progres-
sive aqueous alteration [4]. Nogoya contains several distinct gen-
erations of carbonate minerals; the CM2.3 lithology hosts arago-
nite, calcite and dolomite, whereas the CM2.2 has only calcite.
This is the first time that aragonite has been found in close asso-
ciation with dolomite in a CM meteorite, and the first description 
of dolomite within a CM2.3. The presence of two differently al-
tered lithologies within Nogoya can be explained either by fine-
scale contrasts in alteration conditions (i.e. ice content, porosity) 
or by mixing of clasts from different parent body regions. We 
favour the former possibility; that the parent body contained 
small isolated regions (a few hundred microns) of contrasting 
porosity and water content, producing matrices with different Mg 
concentrations and carbonate mineralogies.
      Acknowledgements: Natural History Museum (London).
      References: [1] McSween H. Y. 1979. Geochimica et Cos-
mochimica Acta 43: 1761-1770. [2] Rubin A. E. et al. 2007. 
Geochimica et Cosmochimica Acta 71: 2361-2382. [3] Howard 
K. T. et al. 2011. Geochimica et Cosmochimica Acta 75: 2735-
2751. [4] Zolensky, M. et al. 1993. Geochimica et Cosmochimica 
Acta 57: 3123-3148.
5041.pdf77th Annual Meteoritical Society Meeting (2014)


Three phases of carbonate minerals and two degrees of alteration in the Nogoya CM2 carbonaceous chondrite

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Three phases of carbonate minerals and two degrees of alteration in the Nogoya CM2 carbonaceous chondrite

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