CM chondrites are highly hydrated

meteorites associated with a parent asteroid that has

experienced significant aqueous processing. The meteoritic

evidence indicates that these non-differentiated

asteroids are formed by fine-grained minerals embedded

in a nanometric matrix that preserves chemical

clues of the forming environment. So far there are two

hypothesis to explain the presence of hydrated minerals

in the content of CM chondrites: one is based on textural

features in chondrule-rim boundaries [1-3], and

the other ‘preaccretionary’ hypothesis proposes the

incorporation of hydrated phases from the protoplanetary

disk [4-6]. The highly porous structure of these

chondrites is inherited from the diverse materials present

in the protoplanetary disk environment. These

bodies were presumably formed by low relative velocity

encounters that led to the accretion of silicate-rich

chondrules, refractory Ca- and Al-rich inclusions

(CAIs), metal grains, and the fine-grained materials

forming the matrix. Owing to the presence of significant

terrestrial water in meteorite finds [7], here we

have focused on two CM chondrite falls with minimal

terrestrial processing: Murchison and Cold Bokkeveld.

Anhydrous carbonaceous chondrite matrices are usually

represented by highly chemically unequilibrated

samples that contain distinguishable stellar grains.

Other chondrites have experienced hydration and

chemical homogeneization that reveal parent body

processes. We have studied CM chondrites because

these meteorites have experienced variable hydration

levels [8-10]. It is important to study the textural effects

of aqueous alteration in the main minerals to

decipher which steps and environments promote bulk

chemistry changes, and create the distinctive alteration

products. It is thought that aqueous alteration has particularly

played a key role in modifying primordial

bulk chemistry, and homogenizing the isotopic content

of fine-grained matrix materials [7, 11, 12]. Fortunately,

the mineralogy produced by parent-body and terrestrial

aqueous alteration processes is distinctive [5, 11]

Abad, M.M.

Alonso-Azcárate, J.

Lee, M.R.

Trigo-Rodríguez, J.M.

English

Enlighten: Publications

  
 
 
Trigo-Rodríguez, J.M., Alonso-Azcárate, J., Abad, M.M., and Lee, 
M.R. (2015) Ultra High Resolution Transmission Electron Microscopy of 
Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body 
Aqueous Processing? In: 46th Lunar and Planetary Science Conference, 
The Woodlands, TX, USA, 16-20 Mar 2015. 
 
 
Copyright © 2015 The Authors 
 
 
http://eprints.gla.ac.uk/102435/  
 
 
 
 
 
Deposited on:  10 February 2015 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Enlighten – Research publications by members of the University of Glasgow 
http://eprints.gla.ac.uk 
ULTRA HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY OF MATRIX MINERAL 
GRAINS IN CM CHONDRITES: PREACCRETIONARY OR PARENT BODY AQUEOUS PROCESSING?  
J.M. Trigo-Rodríguez1, J. Alonso-Azcárate2, M. M. Abad3, and M. R. Lee4, 1Meteorites, Minor Bodies, and Plane-
tary Sciences Group, Institute of Space Sciences (CSIC-IEEC). Campus UAB, Fac. Ciències, C5-p2, 08193 Bellate-
rra (Barcelona), Spain (trigo@ice.csic.es). 2Universidad de Castilla-La Mancha (UCLM), Campus Fábrica de Armas, 
45071 Toledo, Spain. 3Centro de Instrumentación Científica (CIC), Universidad de Granada, 18071 Granada, Spain. 
4School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK. 
 
Introduction:  CM chondrites are highly hydrated 
meteorites associated with a parent asteroid that has 
experienced significant aqueous processing. The mete-
oritic evidence indicates that these non-differentiated 
asteroids are formed by fine-grained minerals embed-
ded in a nanometric matrix that preserves chemical 
clues of the forming environment. So far there are two 
hypothesis to explain the presence of hydrated minerals 
in the content of CM chondrites: one is based on tex-
tural features in chondrule-rim boundaries [1-3], and 
the other ‘preaccretionary’ hypothesis proposes the 
incorporation of hydrated phases from the protoplane-
tary disk [4-6]. The highly porous structure of these 
chondrites is inherited from the diverse materials pre-
sent in the protoplanetary disk environment. These 
bodies were presumably formed by low relative veloci-
ty encounters that led to the accretion of silicate-rich 
chondrules, refractory Ca- and Al-rich inclusions 
(CAIs), metal grains, and the fine-grained materials 
forming the matrix. Owing to the presence of signifi-
cant terrestrial water in meteorite finds [7], here we 
have focused on two CM chondrite falls with minimal 
terrestrial processing: Murchison and Cold Bokkeveld. 
Anhydrous carbonaceous chondrite  matrices are usual-
ly represented by highly chemically unequilibrated 
samples that contain distinguishable stellar grains. 
Other chondrites have experienced hydration and 
chemical homogeneization that reveal parent body 
processes. We have studied CM chondrites because 
these meteorites have experienced variable hydration 
levels [8-10]. It is important to study the textural ef-
fects of aqueous alteration in the main minerals to 
decipher which steps and environments promote bulk 
chemistry changes, and create the distinctive alteration 
products. It is thought that aqueous alteration has par-
ticularly played a key role in modifying primordial 
bulk chemistry, and homogenizing the isotopic content 
of fine-grained matrix materials [7, 11, 12]. Fortunate-
ly, the mineralogy produced by parent-body and terres-
trial aqueous alteration processes is distinctive [5, 11].  
 
     Experimental procedure:  First of all, the meteor-
ite sections were thinned in a ring as usually made for 
TEM studies using a Fischione 1050 ion mill at CIC 
(Granada University). The sample was bombarded with 
energetic ions or neutral atoms (Ar), removing sample 
material until the film was sufficiently thin to study by 
TEM. The result is a thinned ring that is cleaned to 
remove away the remaining amorphous materials and 
then analyzed by UHRTEM (ultra high resolution 
transmission electron microscopy). The study was 
performed using a FEI Titan G2 60-300 microscope 
available at CIC with a high brightness electron gun 
(X-FEG) operated at 300 kV and equipped with a Cs 
image corrector (CEOS) and for analytical electron 
microscopy (AEM) a SUPER-X silicon-drift window-
less EDX detector. The AEM spectra were collected in 
STEM (Scaning Transmission Electron Microscopy) 
mode using a HAADF (High Angle Annular Dark 
Field) detector. Digital X-Ray maps were also collect-
ed on selected areas of the samples. For quantitative 
micro-analyses, EDX data were corrected by the thin-
film method [12-13]. The K-factors were determined 
using mineral standards. These samples were prepared 
as a Canada balsam-mounted thin sections, were 
thinned using a Fischione 1050 model ion mill, and 
carbon coated for TEM observation with the Titan 
microscope. Atomic concentration ratios were convert-
ed into formulae according to stoichiometry (number of 
O atoms in theoretical formulae). 
 
Results and discusion: As found in previous stud-
ies [2], Murchison matrix is composed of very hetero-
geneous materials even at the nanoscale. From the 
different imagery obtained we have selected some 
examples to illustrate the level of complexity found. 
Figure 1 shows a 1 µm window of the Murchison ma-
trix where the center includes a  phase with the charac-
teristic layering of phylosilicates oriented perpendicu-
larly to the line of sight. This figure includes small 
numbered boxes where several EDX spectra were 
taken. Serpentine in its variety of lizardite is repre-
sentative of boxes #1 and 4, but in #2 and 3 we found a 
mixture of serpentine with cronstedtite. Other minerals 
tentatively identified from their EDX spectra are:  #5,6 
pentlandite, #8 carbonate or sulphate, #11 pyrrhotite, 
and #12 pyroxene. In general the presence of these 
minerals exemplify an extraordinary diversity in CM2 
chondrite Murchison. We think this complexity at 
nanoscale might be indicative of the formation condi-
tions of this meteorite, and the little thermal processing 
occurred in its parent asteroid. 
1198.pdf46th Lunar and Planetary Science Conference (2015)
 
Figure 1. HAADF image showing a serpentine-
cronstedtite intergrowth phase surrounded by other 
minerals discussed in the text. 
 
 
Figure 2. Diffraction pattern of lizardite found in 
box #4 (see Fig. 1). 
 
Preliminary conclusions: A comprehensive study 
of the mineral phases of CM chondrites at nanoscale 
can provide important new information regarding their 
textural relationships and origins. We wish to answer 
key questions, for example was organic complexity 
associated with catalytic processes promoted by aque-
ous alteration of some specific minerals? 
We have found that Murchison matrix is exception-
ally complex at the nanoscale. The existence of heavily 
aqueously altered minerals in close contact with anhy-
drous ones is remarkable. This could support by itself 
the idea of a wet accretion of some components of CM 
chondrites. Was this diversity a consequence of several 
stages in the accretion of chondritic parent bodies? [5]. 
On the other hand, Cold Bokkeveld has been more 
extensively aqueously alterered, as revealed by extend-
ed phyllosilicates all over our sample. In any case, as 
Cold Bokkeveld is a breccia it is difficult to reach 
general conclusions. Some minerals, like e.g. sulphates 
were formed in the parent bodies [14]. Future analyti-
cal work will enable us to be more precise about the 
conditions in which such extensive alteration took 
place. We previously concluded that aqueous alteration 
differences among CMs were the result of contrasts in 
the degree of collisional or burial compaction in the 
parent body [7,8]. This was also pointed out from the 
preferred orientation of the dominant serpentine phase 
[15]. This alteration has important implications in other 
areas like e.g. the reflectance diversity found in D-type 
asteroids. The growth of minerals of aqueous alteration 
in the pores of these carbonaceous chondrites [7] could 
have had a deep effect in decreasing the reflectivity of 
their hydrated parent bodies [16].  
 
Acknowledgements: Finantial support from the 
Spanish MEC (research project AYA2011-26522). 
References: [1] Bunch T.E. and Chang S. (1980) 
Geochim. Cosmochim. Acta 44, 1543. [2] Zolensky M. 
and McSween H.Y. (1988) In Meteorites and the Early 
Solar System, Univ. Arizona press, Tucson, p. 114. [3] 
Browning et al. (1996) Geochim. Cosmochim. Acta 60, 
2621. [4] Metzler K. et al. (1992) Geochim. Cosmo-
chim. Acta 56, 2873. [5] Bischoff A. (1998) Meteorit. 
Planet. Sci. 33, 1113. [6] Hanowski N.P. and Brearley 
A.J. (2000) Meteorit. Planet. Sci. 35, 1291. [7] Trigo-
Rodríguez J.M. et al. (2006) Geochim. Cosmochim. 
Acta 70, 1271. [8] Rubin A.E. et al. (2007) Geochim. 
Cosmochim. Acta 71, 2361. [9] Bland P. et al. (2006) 
in Meteorites and the Early Solar System II, D.S. Lau-
retta & H.Y. McSween Jr. (eds.), Univ. Arizona Press, 
Tucson,  853. [10] Zolensky M.E. et al. (1993) Geo-
chim. Cosmochim. Acta 57, 3123. [11] Brearley A. and 
Jones R.H. (1998) In Planetary Materials, ed. Papike 
J.J., Washington, D.C.: Min. Soc. of America, 1-398. 
[12] Cliff G. and Lorimer G.W. (1975) J. Microscopy 
103, 207. [13] Lorimer G.W. and Cliff G. (1976) In 
Electron Microscopy in Mineralogy, Springer-Verlag, 
Berlin, 506. [14] Lee M.R. (1993) Meteoritics 28, 53. 
[15] Fujimura A. et al. (1983) Earth Planet. Sci. Lett. 
66, 25. [16] Trigo-Rodríguez J.M. et al. (2013) 
MNRAS, 437, 227-240. [17] Brearley A.J. (2006) in 
Meteorites and the Early Solar System II, D.S. Lauretta 
& H.Y. McSween Jr. (eds.), Univ. Arizona Press, Tuc-
son,  587-624.  
1198.pdf46th Lunar and Planetary Science Conference (2015)


Ultra High Resolution Transmission Electron Microscopy of Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body Aqueous Processing?

Enlighten

    Trigo-Rodríguez, J.M., Alonso-Azcárate, J., Abad, M.M., and Lee, M.R. (2015) Ultra High Resolution Transmission Electron Microscopy of Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body Aqueous Processing? In: 46th Lunar and Planetary Science Conference, The Woodlands, TX, USA, 16-20 Mar 2015.   Copyright © 2015 The Authors   http://eprints.gla.ac.uk/102435/       Deposited on:  10 February 2015                  Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk ULTRA HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY OF MATRIX MINERAL GRAINS IN CM CHONDRITES: PREACCRETIONARY OR PARENT BODY AQUEOUS PROCESSING?  J.M. Trigo-Rodríguez1, J. Alonso-Azcárate2, M. M. Abad3, and M. R. Lee4, 1Meteorites, Minor Bodies, and Plane-tary Sciences Group, Institute of Space Sciences (CSIC-IEEC). Campus UAB, Fac. Ciències, C5-p2, 08193 Bellate-rra (Barcelona), Spain (trigo@ice.csic.es). 2Universidad de Castilla-La Mancha (UCLM), Campus Fábrica de Armas, 45071 Toledo, Spain. 3Centro de Instrumentación Científica (CIC), Universidad de Granada, 18071 Granada, Spain. 4School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK.  Introduction:  CM chondrites are highly hydrated meteorites associated with a parent asteroid that has experienced significant aqueous processing. The mete-oritic evidence indicates that these non-differentiated asteroids are formed by fine-grained minerals embed-ded in a nanometric matrix that preserves chemical clues of the forming environment. So far there are two hypothesis to explain the presence of hydrated minerals in the content of CM chondrites: one is based on tex-tural features in chondrule-rim boundaries [1-3], and the other ‘preaccretionary’ hypothesis proposes the incorporation of hydrated phases from the protoplane-tary disk [4-6]. The highly porous structure of these chondrites is inherited from the diverse materials pre-sent in the protoplanetary disk environment. These bodies were presumably formed by low relative veloci-ty encounters that led to the accretion of silicate-rich chondrules, refractory Ca- and Al-rich inclusions (CAIs), metal grains, and the fine-grained materials forming the matrix. Owing to the presence of signifi-cant terrestrial water in meteorite finds [7], here we have focused on two CM chondrite falls with minimal terrestrial processing: Murchison and Cold Bokkeveld. Anhydrous carbonaceous chondrite  matrices are usual-ly represented by highly chemically unequilibrated samples that contain distinguishable stellar grains. Other chondrites have experienced hydration and chemical homogeneization that reveal parent body processes. We have studied CM chondrites because these meteorites have experienced variable hydration levels [8-10]. It is important to study the textural ef-fects of aqueous alteration in the main minerals to decipher which steps and environments promote bulk chemistry changes, and create the distinctive alteration products. It is thought that aqueous alteration has par-ticularly played a key role in modifying primordial bulk chemistry, and homogenizing the isotopic content of fine-grained matrix materials [7, 11, 12]. Fortunate-ly, the mineralogy produced by parent-body and terres-trial aqueous alteration processes is distinctive [5, 11].        Experimental procedure:  First of all, the meteor-ite sections were thinned in a ring as usually made for TEM studies using a Fischione 1050 ion mill at CIC (Granada University). The sample was bombarded with energetic ions or neutral atoms (Ar), removing sample material until the film was sufficiently thin to study by TEM. The result is a thinned ring that is cleaned to remove away the remaining amorphous materials and then analyzed by UHRTEM (ultra high resolution transmission electron microscopy). The study was performed using a FEI Titan G2 60-300 microscope available at CIC with a high brightness electron gun (X-FEG) operated at 300 kV and equipped with a Cs image corrector (CEOS) and for analytical electron microscopy (AEM) a SUPER-X silicon-drift window-less EDX detector. The AEM spectra were collected in STEM (Scaning Transmission Electron Microscopy) mode using a HAADF (High Angle Annular Dark Field) detector. Digital X-Ray maps were also collect-ed on selected areas of the samples. For quantitative micro-analyses, EDX data were corrected by the thin-film method [12-13]. The K-factors were determined using mineral standards. These samples were prepared as a Canada balsam-mounted thin sections, were thinned using a Fischione 1050 model ion mill, and carbon coated for TEM observation with the Titan microscope. Atomic concentration ratios were convert-ed into formulae according to stoichiometry (number of O atoms in theoretical formulae).  Results and discusion: As found in previous stud-ies [2], Murchison matrix is composed of very hetero-geneous materials even at the nanoscale. From the different imagery obtained we have selected some examples to illustrate the level of complexity found. Figure 1 shows a 1 µm window of the Murchison ma-trix where the center includes a  phase with the charac-teristic layering of phylosilicates oriented perpendicu-larly to the line of sight. This figure includes small numbered boxes where several EDX spectra were taken. Serpentine in its variety of lizardite is repre-sentative of boxes #1 and 4, but in #2 and 3 we found a mixture of serpentine with cronstedtite. Other minerals tentatively identified from their EDX spectra are:  #5,6 pentlandite, #8 carbonate or sulphate, #11 pyrrhotite, and #12 pyroxene. In general the presence of these minerals exemplify an extraordinary diversity in CM2 chondrite Murchison. We think this complexity at nanoscale might be indicative of the formation condi-tions of this meteorite, and the little thermal processing occurred in its parent asteroid. 1198.pdf46th Lunar and Planetary Science Conference (2015) Figure 1. HAADF image showing a serpentine-cronstedtite intergrowth phase surrounded by other minerals discussed in the text.   Figure 2. Diffraction pattern of lizardite found in box #4 (see Fig. 1).  Preliminary conclusions: A comprehensive study of the mineral phases of CM chondrites at nanoscale can provide important new information regarding their textural relationships and origins. We wish to answer key questions, for example was organic complexity associated with catalytic processes promoted by aque-ous alteration of some specific minerals? We have found that Murchison matrix is exception-ally complex at the nanoscale. The existence of heavily aqueously altered minerals in close contact with anhy-drous ones is remarkable. This could support by itself the idea of a wet accretion of some components of CM chondrites. Was this diversity a consequence of several stages in the accretion of chondritic parent bodies? [5]. On the other hand, Cold Bokkeveld has been more extensively aqueously alterered, as revealed by extend-ed phyllosilicates all over our sample. In any case, as Cold Bokkeveld is a breccia it is difficult to reach general conclusions. Some minerals, like e.g. sulphates were formed in the parent bodies [14]. Future analyti-cal work will enable us to be more precise about the conditions in which such extensive alteration took place. We previously concluded that aqueous alteration differences among CMs were the result of contrasts in the degree of collisional or burial compaction in the parent body [7,8]. This was also pointed out from the preferred orientation of the dominant serpentine phase [15]. This alteration has important implications in other areas like e.g. the reflectance diversity found in D-type asteroids. The growth of minerals of aqueous alteration in the pores of these carbonaceous chondrites [7] could have had a deep effect in decreasing the reflectivity of their hydrated parent bodies [16].   Acknowledgements: Finantial support from the Spanish MEC (research project AYA2011-26522). References: [1] Bunch T.E. and Chang S. (1980) Geochim. Cosmochim. Acta 44, 1543. [2] Zolensky M. and McSween H.Y. (1988) In Meteorites and the Early Solar System, Univ. Arizona press, Tucson, p. 114. [3] Browning et al. (1996) Geochim. Cosmochim. Acta 60, 2621. [4] Metzler K. et al. (1992) Geochim. Cosmo-chim. Acta 56, 2873. [5] Bischoff A. (1998) Meteorit. Planet. Sci. 33, 1113. [6] Hanowski N.P. and Brearley A.J. (2000) Meteorit. Planet. Sci. 35, 1291. [7] Trigo-Rodríguez J.M. et al. (2006) Geochim. Cosmochim. Acta 70, 1271. [8] Rubin A.E. et al. (2007) Geochim. Cosmochim. Acta 71, 2361. [9] Bland P. et al. (2006) in Meteorites and the Early Solar System II, D.S. Lau-retta & H.Y. McSween Jr. (eds.), Univ. Arizona Press, Tucson,  853. [10] Zolensky M.E. et al. (1993) Geo-chim. Cosmochim. Acta 57, 3123. [11] Brearley A. and Jones R.H. (1998) In Planetary Materials, ed. Papike J.J., Washington, D.C.: Min. Soc. of America, 1-398. [12] Cliff G. and Lorimer G.W. (1975) J. Microscopy 103, 207. [13] Lorimer G.W. and Cliff G. (1976) In Electron Microscopy in Mineralogy, Springer-Verlag, Berlin, 506. [14] Lee M.R. (1993) Meteoritics 28, 53. [15] Fujimura A. et al. (1983) Earth Planet. Sci. Lett. 66, 25. [16] Trigo-Rodríguez J.M. et al. (2013) MNRAS, 437, 227-240. [17] Brearley A.J. (2006) in Meteorites and the Early Solar System II, D.S. Lauretta & H.Y. McSween Jr. (eds.), Univ. Arizona Press, Tuc-son,  587-624.  1198.pdf46th Lunar and Planetary Science Conference (2015)

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Ultra High Resolution Transmission Electron Microscopy of Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body Aqueous Processing?

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