MISIP-2024 Project-2 – Interactions between minerals and organic matter in carbonaceouschondrites.
Maaya Hamaguchi 1 , Louis-Alexandre Lobanov 2 , Daisy Lumley-Curtis 3 , Grace
Purnell 4
1

Kyoto Prefectural University, 2 Birkbeck, University of London,Manchester, 4 Durham University

3

University ofIn carbonaceous chondrites, organic matter is a subject of extensive study due to its role in theevolution of the solar system and its relevance to the origin of life on Earth, as these types of primitive
meteorites may have helped to deliver organic material to the early Earth. They give an insight into thecomposition of the early Solar System as well as the Ryugu and Bennu asteroids as the composition ofthe asteroids resembles CI chondrites. We studied the interaction between organic matter and minerals,focusing on phyllosilicates and carbonates. The samples investigated were two CM chondrites,
Murchison and Aguas Zarcas, and one CI chondrite, Orgueil. Equipment such as SEM-EDS, Raman
spectroscopy, SIMS, and IRMS was used to look at the textures and composition of sites on the surfaceof the samples.
While investigating the phyllosilicate textures in Aguas Zarcas, Murchison and Orgueil, it wasseen that Aguas Zarcas and Murchison are very heterogenous compared to Orgueil. The phyllosilicateswere investigated using SEM-EDS and we found that there is a significant separation between the CIand CM phyllosilicates. Orgueil’s matrix appears to be an intermix of Serpentine and Saponite andAguas Zarcas and Murchison seem to have a mixture of Cronstedtite, Serpentine and Tochilinite in theirmatrix. This is consistent with previous findings. The matrix of Aguas Zarcas plotted in 2 distinct
populations corresponding to light and dark areas of the matrix with the populations differing in Fe/Siratio.
We set out to characterise the organic signatures using a micro-Raman spectrometer. We discoveredthat there were positive correlation trends between the D-band centre and the D-band FWHM in all 3
meteorites with Aguas Zarcas and Murchison plotting together and a clear separation with Orgueil. Thisappears to be a distinction between CM2 and CI1 meteorites. Orgueil plotted higher on both, further
along on the same trendline that the CM2s show. This could be due to increased aqueous alteration. For
the organic G-band peaks, we plotted G-band centre against G-band FWHM. In both Aguas Zarcas andMurchison, there is a clear separation by G-band centre value into 2 populations for the different areas
analysed. This has not been observed before. Orgueil only has a single population trend, with a similar
gradient. This single trend corresponds to the high G-band centre trend visible in the CM2 chondrites.
The 2 population trends in the Aguas Zarcas and Murchison samples present as 2 trends of negative
correlation that are semi-parallel, with the high G-centre trend usually presenting a steeper trend. The
negative correlation line of the trends is thought to be a result of irradiation or heating. These populationsof high and low G-band centre do not correlate with light and dark areas of the matrix, indicating thatphyllosilicate texture is likely not the control on the organic matter populations. The populations in both
the Murchison and Aguas Zarcas samples do however cluster into regions on the sample, resembling
different compositional areas. Due to their lack of correlation with matrix textures, we believe that the2 populations of organics present in Aguas Zarcas and Murchison could represent 2 distinct
compositions of organics in their parent body. The heterogeneity could pre-date the parent body andwould in this model be due to poor intermixing of the different organic populations accreted onto theCM2 parent body.
There was a distinction in composition between the carbonates seen in Orgueil, dolomite andmagnesite, as compared with Aguas Zarcas and Murchison, in which only calcite was seen. Somecarbonates were found to have strong interactions with the organic matter. Organic matter was found as
an inclusion within an Aguas Zarcas calcite. This may have been a result of the carbonate forming
around a pyroxene or CAI precursor aggregate, which was associated with organic matter and ice,containing water and possibly CO2. Associated within a carbonate clast in Murchison is a zone ofphyllosilicate with an unusually high calcium content, possibly smectite and high aluminium content
relative to the matrix. This leads us to the conclusion that this carbonate grain may have formed from aCAI precursor. Another carbonate in Murchison is associated with a large grain of organic matter, which

due to matching carbon isotopes on SIMS, may have served as the source for the formation of thecarbonate grain. The conclusion of the carbonate investigation is that OM-rich dust grains react with ice
to form a CO2 heavy fluid, which in turn reacts with Ca-rich phases to form carbonates.
Using SIMS, we determined that Aguas Zarcas and Murchison plot as 2 distinct populations
separated along δ2H, while having similar δ15N and δ13C. Organic matter grains were found in
Murchison and analysed. These have very high δ15N (around 250 ‰) and δ13C (around 60-75 ‰). Thissuggests that the source of these isotopes is primordial, deriving from the pre-accretionary isotopic
signatures of the organic matter. The carbonates have similarly high δ13C isotopes suggesting they could
have formed from the organic matter. The light and dark phyllosilicate areas were also investigated forisotopic signature. In Aguas Zarcas, the light and dark areas of the matrix are separated by δ15N, withthe darker areas having a higher δ15N. This is likely due to the dark areas of the matrix being richer inorganic matter relative to the light ones. On the other hand, in Murchison the light and dark areas havesimilar δ15N but are separated along the δ2H axis. The darker areas have a higher δ2H. One model toexplain this is that the lighter areas potentially had greater aqueous alteration from water ice, which isdepleted in δ2H, because of varying amounts of ice through the meteorite, resulting in a lower δ2H andthe formation of tochilinite.
Altogether, this study reveals some interesting insights into the processes that governed the earlysolar system and offers ample opportunity for follow-up research to understand the relationship between
phyllosilicates, carbonates and organic matter in carbonaceous chondrites.