Evidence from the Lafayette meteorite shows that carbon dioxide could have been sequestered very effectively from the martian atmosphere by mineral carbonation

Lee, M.R.

Mark, D.F.

Stuart, F.M.

Tomkinson, T.

English

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Tomkinson, T., Lee, M.R., Mark, D.F., and Stuart, F.M. (2013) The nakhlite 
meteorites provide evidence for mineralization of martian CO2 by carbonation of 
silicates. In: 44th Lunar and Planetary Science Conference, 18-22 Mar 2013, 
Texas, TX, USA. 
 
 
Copyright © 2013 The Authors 
 
 
A copy can be downloaded for personal non-commercial research or 
study, without prior permission or charge 
 
Content must not be changed in any way or reproduced in any format 
or medium without the formal permission of the copyright holder(s) 
 
 
When referring to this work, full bibliographic details must be given 
 
 
  
http://eprints.gla.ac.uk/77518 
 
 
 
Deposited on:  10 September 2014 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Enlighten – Research publications by members of the University of Glasgow 
http://eprints.gla.ac.uk 
THE NAKHLITE METEORITES PROVIDE EVIDENCE FOR MINERALIZATION OF MARTIAN CO2 
BY CARBONATION OF SILICATES.  T. Tomkinson1, M. R. Lee2, D. F. Mark1, F. M. Stuart1. 1Scottish Univer-
sities Environmental Research Centre, East Kilbride E75 0QF, U.K. E-mail: tim.tomkinson@glasgow.ac.uk., 
2School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ U.K. 
 
Introduction: Climate models suggest that the 
Noachian atmosphere of Mars could have been CO2-
rich and much thicker than at the present-day [1, 2]. 
These predictions can be tested by attempting to locate 
the ‘missing’ CO2. Numerous mechanisms for the loss 
of CO2 from the planet’s early atmosphere have been 
proposed, including escape to space, trapping as ice 
and clathrates, and storage in carbonate deposits [3-6]. 
The latter scenario is supported by the detection of 
carbonates within Martian dust, bedrock outcrops and 
meteorites [6-11]. However, the volumes so far located 
are insufficient to account for all the CO2 that is pre-
dicted to have been once present within the atmos-
phere. 
Here we propose that large quantities of CO2 were 
removed from the Noachian atmosphere and stored in 
the crust by ‘carbonation’. This is a water-mediated 
reaction whereby silicate minerals that are rich in diva-
lent cations (e.g. olivine) are replaced by carbonates; 
on Earth carbonation of ultrabasic and basic rocks is an 
efficient way to irreversibly sequester CO2. For exam-
ple, the carbonation of terrestrial basalt consumes 
~1.8×108 tons CO2 yr-1 globally [12], and if all of the 
peridotite in the Samail ophiolite of Oman was con-
verted to carbonate it would consume 77 trillion tons 
of CO2 [13]. 
Our study has used the nakhlite meteorite Lafayette 
as an analogue for the Noachian crust. Lafayette is an 
Amazonian olivine-bearing clinopyroxenite that con-
tains a suite of secondary minerals, principally car-
bonates and hydrous silicates, that crystallized from 
liquid water [14]. 
Methods: A carbon coated thin section of Lafa-
yette was studied using a FEI Quanta field-emission 
SEM equipped with an EDAX Genesis energy-
dispersive X-ray spectrometer (EDX) and TSL elec-
tron backscatter diffraction (EBSD) system. Backscat-
tered electron (BSE) images were obtained at 20 kV 
and under high vacuum. The crystallographic orienta-
tion of the olivine grains was determined by EBSD 
mapping at low vacuum (~50-70 Pa), 20 kV, and with 
a relatively high beam current. Kikuchi patterns were 
acquired at a rate of ~20 patterns/sec. and at a step size 
of ~0.3 µm. The patterns were indexed using the struc-
ture file for olivine in the TSL database. 
      Results: The Lafayette carbonates occur within 
serrated veins that cross-cut olivine grains (Fig. 1A), 
and are also present within the mesostasis. The axes of 
most of the olivine-hosted veins are oriented parallel to 
(001)olivine. The veins contain Ca-siderite 
(Ca0.31Mn0.24Fe0.45CO3), several generations of 
phyllosilicates that can be distinguished from each 
other in BSE images by contrasts in their crystal size, 
and Fe-oxides (Fig. 2). The siderite is always in con-
tact with olivine, and occurs either between closely-
spaced veins (Fig. 1B) or it fills coarse serrations on 
vein walls (Fig. 2). The geometry of the siderite-
olivine interface is controlled by the olivine crystal 
structure and is typically parallel to {111}. 
 
 
 
Figure 1: BSE images of olivine-hosted secondary 
mineral veins. [A] Part of an olivine grain (O) sur-
rounded by augite (medium grey). The olivine is cross-
cut by veins with coarsely serrated walls whose axes 
lie parallel to olivine (001). [B] An ‘island’ of olivine 
(O) between two veins that has been partially replaced 
by siderite (S). Among the constituents of the veins is 
phyllosilicate (P) and films of Fe-oxide (white). 
 
Siderite is always intergrown with a coarsely crystal-
line phyllosilicate, and the petrographic relationships 
between the two minerals show that the phyllosilicate 
has replaced the carbonate [14, 15]. The axes of the 
veins are occupied by films of Fe-oxide (Fig. 1B) and 
nanocrystalline smectite. 
Discussion: The petrographic relationships be-
tween  Ca-siderite and olivine indicate that the car-
bonate has replaced the silicate, and the sequence of 
1208.pdf44th Lunar and Planetary Science Conference (2013)
events is shows schematically in Figure 2. The siderite 
is inferred to have replaced the walls of an 
intracrystalline sheet  pore (Fig. 2A), and the trajectory 
of the reaction interface was controlled by the olivine 
crystal structure (Fig. 2B). A very similar sawtooth 
interface between terrestrial olivine and replacive Ca-
Mg carbonates has been previously observed [16]. The 
limited degree of replacement of olivine suggests that 
siderite crystallized for only a brief period of time. 
Following exhaustion of carbonate anions, the car-
bonate was partially or completely replaced by 
phyllosilicates, again working inwards from the vein 
axis (Fig. 2C). In narrow veins all of the siderite has 
been replaced by phyllosilicate so that it survives only 
within the deepest notches of coarser veins (Fig. 2C). 
 Figure 2: Edited backscatter electron (BSE) images of 
a secondary mineral vein within olivine (O) showing 
its sequence of formation. [A] Generation of (001)-
parallel sheet pores by dissolution/fracturing. [B] For-
mation of siderite by crystallographically controlled 
replacement of olivine. [C] Replacement of siderite by 
phyllosilicate (P), working inwards from the vein axis. 
Implications: Lafayette provides direct evidence 
for carbonation of the Martian crust. On Earth this re-
action can be initiated by the exposure of soluble sili-
cate minerals such as olivine to carbonic acid-rich so-
lutions. Dissolution of olivine supersaturates solutions 
at the reaction interface with respect to the carbonate 
by simultaneously increasing their pH value and liber-
ating divalent cations [17]. Given the composition of 
Lafayette olivine (~Fa67), it may be expected that the 
replacive carbonates would have been Fe- and Mg-
rich, yet the siderite contains Ca and Mn, and is almost 
devoid of Mg. Therefore the solutions that mediated 
replacement must have imported carbonate anions, Ca 
and Mn to the reaction interface, and exported Mg. 
However, enrichment in Ca and depletion of Mg is 
commonplace in the carbonation of terrestrial olivine-
rocks, and is due to kinetic inhibition of magnesite 
crystallization owing to hydration of Mg ions [17].  
Large volumes of carbonate did not form in the 
nakhlite parent rock owing to the paucity of water and 
carbonate anions. However, we predict that carbona-
tion would have been far more efficient and wide-
spread in the Noachian crust if the atmosphere had 
been warmer, wetter and richer in CO2. Crucially how-
ever Lafayette shows that the carbonates selectively 
replace olivine over other silicates owing to its much 
higher solubility. Therefore, the Noachian carbonates 
may be finely disseminated throughout the Martian 
crust and so difficult to detect by orbiters and rovers. 
Acknowledgments: We thank Tim McCoy (Divi-
sion of Meteorites, Smithsonian Institution) for provid-
ing the sample used in this study. This work was sup-
ported by the UK Science and Technology Facilities 
Council (grants ST/H002472/1 and ST/H002960/1). 
References: [1] Pollack, J. B. et al. (1987) Icarus, 
71, 203–224. [2] Jakosky, B. M. and Phillips, R. J. 
(2001) Nature, 412, 237–244. [3] Leblanc, F. and 
Johnson, R. E. (2002) J. Geophys. Res., 107, E2. [4] 
Kass, D. M. and Yung, Y. L. (1995) Science, 268, 
697–699. [5] Phillips, R. J. et al. (2011) Science, 332, 
838–841. [6] Harvey. R. P. (2010) Science, 329, 400–
401. [7] Bandfield J. L. et al. (2003) Science, 301, 
1084–1087. [8] Ehlmann B. L. et al. (2008) Science, 
322, 1828–1832. [9] Morris R. V. et al. (2010) Science, 
329, 421-424. [10] Michalski, J. R. Niles P. B. (2010) 
Nature Geosci., 3, 751–755. [11] Wray J. J. et al. 
(2011) LPSC 42, Abstract #2635. [12] Dessert C. et al. 
(2003) Chem. Geol.,  202, 257–273. [13] Kelemen, P. 
B. and Matter, J. (2008) Proc. National Academy of 
Sciences, 105, 17295–17300. [14] Treiman A. H. 
(1993) Geochim. Cosmochim. Acta, 57, 4753–4767. 
[15] Changela, H. G. and Bridges J. C. (2011) 
Meteoritics & Planet. Sci., 45, 1847–1867. [16] 
Adreani, M. et al. (2009) Environment. Sci. and Tech., 
43, 1226–1231. [17] Hovelmann, A. et al. (2010)  
Geochim. Cosmochim. Acta, 74, 6935–6964. 
1208.pdf44th Lunar and Planetary Science Conference (2013)


The nakhlite meteorites provide evidence for mineralization of martian CO2 by carbonation of silicates

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    Tomkinson, T., Lee, M.R., Mark, D.F., and Stuart, F.M. (2013) The nakhlite meteorites provide evidence for mineralization of martian CO2 by carbonation of silicates. In: 44th Lunar and Planetary Science Conference, 18-22 Mar 2013, Texas, TX, USA.   Copyright © 2013 The Authors   A copy can be downloaded for personal non-commercial research or study, without prior permission or charge  Content must not be changed in any way or reproduced in any format or medium without the formal permission of the copyright holder(s)   When referring to this work, full bibliographic details must be given     http://eprints.gla.ac.uk/77518    Deposited on:  10 September 2014                 Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk THE NAKHLITE METEORITES PROVIDE EVIDENCE FOR MINERALIZATION OF MARTIAN CO2 BY CARBONATION OF SILICATES.  T. Tomkinson1, M. R. Lee2, D. F. Mark1, F. M. Stuart1. 1Scottish Univer-sities Environmental Research Centre, East Kilbride E75 0QF, U.K. E-mail: tim.tomkinson@glasgow.ac.uk., 2School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ U.K.  Introduction: Climate models suggest that the Noachian atmosphere of Mars could have been CO2-rich and much thicker than at the present-day [1, 2]. These predictions can be tested by attempting to locate the ‘missing’ CO2. Numerous mechanisms for the loss of CO2 from the planet’s early atmosphere have been proposed, including escape to space, trapping as ice and clathrates, and storage in carbonate deposits [3-6]. The latter scenario is supported by the detection of carbonates within Martian dust, bedrock outcrops and meteorites [6-11]. However, the volumes so far located are insufficient to account for all the CO2 that is pre-dicted to have been once present within the atmos-phere. Here we propose that large quantities of CO2 were removed from the Noachian atmosphere and stored in the crust by ‘carbonation’. This is a water-mediated reaction whereby silicate minerals that are rich in diva-lent cations (e.g. olivine) are replaced by carbonates; on Earth carbonation of ultrabasic and basic rocks is an efficient way to irreversibly sequester CO2. For exam-ple, the carbonation of terrestrial basalt consumes ~1.8×108 tons CO2 yr-1 globally [12], and if all of the peridotite in the Samail ophiolite of Oman was con-verted to carbonate it would consume 77 trillion tons of CO2 [13]. Our study has used the nakhlite meteorite Lafayette as an analogue for the Noachian crust. Lafayette is an Amazonian olivine-bearing clinopyroxenite that con-tains a suite of secondary minerals, principally car-bonates and hydrous silicates, that crystallized from liquid water [14]. Methods: A carbon coated thin section of Lafa-yette was studied using a FEI Quanta field-emission SEM equipped with an EDAX Genesis energy-dispersive X-ray spectrometer (EDX) and TSL elec-tron backscatter diffraction (EBSD) system. Backscat-tered electron (BSE) images were obtained at 20 kV and under high vacuum. The crystallographic orienta-tion of the olivine grains was determined by EBSD mapping at low vacuum (~50-70 Pa), 20 kV, and with a relatively high beam current. Kikuchi patterns were acquired at a rate of ~20 patterns/sec. and at a step size of ~0.3 µm. The patterns were indexed using the struc-ture file for olivine in the TSL database.       Results: The Lafayette carbonates occur within serrated veins that cross-cut olivine grains (Fig. 1A), and are also present within the mesostasis. The axes of most of the olivine-hosted veins are oriented parallel to (001)olivine. The veins contain Ca-siderite (Ca0.31Mn0.24Fe0.45CO3), several generations of phyllosilicates that can be distinguished from each other in BSE images by contrasts in their crystal size, and Fe-oxides (Fig. 2). The siderite is always in con-tact with olivine, and occurs either between closely-spaced veins (Fig. 1B) or it fills coarse serrations on vein walls (Fig. 2). The geometry of the siderite-olivine interface is controlled by the olivine crystal structure and is typically parallel to {111}.    Figure 1: BSE images of olivine-hosted secondary mineral veins. [A] Part of an olivine grain (O) sur-rounded by augite (medium grey). The olivine is cross-cut by veins with coarsely serrated walls whose axes lie parallel to olivine (001). [B] An ‘island’ of olivine (O) between two veins that has been partially replaced by siderite (S). Among the constituents of the veins is phyllosilicate (P) and films of Fe-oxide (white).  Siderite is always intergrown with a coarsely crystal-line phyllosilicate, and the petrographic relationships between the two minerals show that the phyllosilicate has replaced the carbonate [14, 15]. The axes of the veins are occupied by films of Fe-oxide (Fig. 1B) and nanocrystalline smectite. Discussion: The petrographic relationships be-tween  Ca-siderite and olivine indicate that the car-bonate has replaced the silicate, and the sequence of 1208.pdf44th Lunar and Planetary Science Conference (2013)events is shows schematically in Figure 2. The siderite is inferred to have replaced the walls of an intracrystalline sheet  pore (Fig. 2A), and the trajectory of the reaction interface was controlled by the olivine crystal structure (Fig. 2B). A very similar sawtooth interface between terrestrial olivine and replacive Ca-Mg carbonates has been previously observed [16]. The limited degree of replacement of olivine suggests that siderite crystallized for only a brief period of time. Following exhaustion of carbonate anions, the car-bonate was partially or completely replaced by phyllosilicates, again working inwards from the vein axis (Fig. 2C). In narrow veins all of the siderite has been replaced by phyllosilicate so that it survives only within the deepest notches of coarser veins (Fig. 2C).  Figure 2: Edited backscatter electron (BSE) images of a secondary mineral vein within olivine (O) showing its sequence of formation. [A] Generation of (001)-parallel sheet pores by dissolution/fracturing. [B] For-mation of siderite by crystallographically controlled replacement of olivine. [C] Replacement of siderite by phyllosilicate (P), working inwards from the vein axis. Implications: Lafayette provides direct evidence for carbonation of the Martian crust. On Earth this re-action can be initiated by the exposure of soluble sili-cate minerals such as olivine to carbonic acid-rich so-lutions. Dissolution of olivine supersaturates solutions at the reaction interface with respect to the carbonate by simultaneously increasing their pH value and liber-ating divalent cations [17]. Given the composition of Lafayette olivine (~Fa67), it may be expected that the replacive carbonates would have been Fe- and Mg-rich, yet the siderite contains Ca and Mn, and is almost devoid of Mg. Therefore the solutions that mediated replacement must have imported carbonate anions, Ca and Mn to the reaction interface, and exported Mg. However, enrichment in Ca and depletion of Mg is commonplace in the carbonation of terrestrial olivine-rocks, and is due to kinetic inhibition of magnesite crystallization owing to hydration of Mg ions [17].  Large volumes of carbonate did not form in the nakhlite parent rock owing to the paucity of water and carbonate anions. However, we predict that carbona-tion would have been far more efficient and wide-spread in the Noachian crust if the atmosphere had been warmer, wetter and richer in CO2. Crucially how-ever Lafayette shows that the carbonates selectively replace olivine over other silicates owing to its much higher solubility. Therefore, the Noachian carbonates may be finely disseminated throughout the Martian crust and so difficult to detect by orbiters and rovers. Acknowledgments: We thank Tim McCoy (Divi-sion of Meteorites, Smithsonian Institution) for provid-ing the sample used in this study. This work was sup-ported by the UK Science and Technology Facilities Council (grants ST/H002472/1 and ST/H002960/1). References: [1] Pollack, J. B. et al. (1987) Icarus, 71, 203–224. [2] Jakosky, B. M. and Phillips, R. J. (2001) Nature, 412, 237–244. [3] Leblanc, F. and Johnson, R. E. (2002) J. Geophys. Res., 107, E2. [4] Kass, D. M. and Yung, Y. L. (1995) Science, 268, 697–699. [5] Phillips, R. J. et al. (2011) Science, 332, 838–841. [6] Harvey. R. P. (2010) Science, 329, 400–401. [7] Bandfield J. L. et al. (2003) Science, 301, 1084–1087. [8] Ehlmann B. L. et al. (2008) Science, 322, 1828–1832. [9] Morris R. V. et al. (2010) Science, 329, 421-424. [10] Michalski, J. R. Niles P. B. (2010) Nature Geosci., 3, 751–755. [11] Wray J. J. et al. (2011) LPSC 42, Abstract #2635. [12] Dessert C. et al. (2003) Chem. Geol.,  202, 257–273. [13] Kelemen, P. B. and Matter, J. (2008) Proc. National Academy of Sciences, 105, 17295–17300. [14] Treiman A. H. (1993) Geochim. Cosmochim. Acta, 57, 4753–4767. [15] Changela, H. G. and Bridges J. C. (2011) Meteoritics & Planet. Sci., 45, 1847–1867. [16] Adreani, M. et al. (2009) Environment. Sci. and Tech., 43, 1226–1231. [17] Hovelmann, A. et al. (2010)  Geochim. Cosmochim. Acta, 74, 6935–6964. 1208.pdf44th Lunar and Planetary Science Conference (2013)

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The nakhlite meteorites provide evidence for mineralization of martian CO2 by carbonation of silicates

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