Tracing the earliest stages of hydrothermal alteration on the CM chondrite parent body

1A. J. King,1,2E. Mason,1,3H. C. Bates,1P. F. Schofield,3,4K. L. Donaldson Hanna,3N. E. Bowles,1S. S. Russell
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13734]
1Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD UK
2Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ UK
3Planetary Spectroscopy Facility, Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU UK
4Department of Physics, University of Central Florida, Orlando, Florida, 32816–2385 USA
Published by arrangement with John Wiley & Sons

The CM carbonaceous chondrites are an important resource in our efforts to understand the role of volatiles in the formation of planetary systems. We report the bulk mineralogy, water abundance, and infrared (IR) reflectance spectra of the CM chondrites LaPaz Icefield (LAP) 04514, LAP 04796, LAP 04565, and LAP 02333. They contain abundant Fe- and Mg-rich serpentines (˜70–80 vol%), and based on their phyllosilicate fractions, we classify LAP 04514, LAP 04796, and LAP 04565 as petrologic subtype 1.6 and LAP 02333 as 1.4. This is consistent with estimated water abundances of 9.9 (±1.1) wt% for LAP 04796, 10.4 (±0.1) wt% for LAP 04565, and 11.5 (±0.5) wt% for LAP 02333. However, LAP 04514 contains less water (8.8 ± 0.3 wt%), has a shallower 3 µm band depth, and lacks tochilinite having experienced posthydration temperatures of ˜300–400 °C. We conclude that LAP 04514, LAP 04796, and LAP 04565 are among the least altered CM chondrites, which retain primitive features from the initial building blocks of the CM parent body. Finally, we use the IR spectral features of LAP 04514, LAP 04796, and LAP 04565 to identify C-complex asteroid surfaces that record mild levels of hydration.

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