A Complex Interplay of Heat and Aqueous Alteration Experienced by the Paris CM Chondrite
Bonal L., Beck P., Nakamura T., Enokido Y., Gattacceca J., Eschrig J.
82nd Annual Meeting of The Meteoritical Society 2019
“The Paris meteorite is a CM chondrite [1] that has been thoroughly studied to assess its parent body history. Paris was classified as type 2.7 [2] on the alteration scale defined by [3]. Paris is brecciated and petrographically heterogeneous, with distinct lithologies (typically metal-rich and metal-poor, [4]) having experienced various degrees of alteration [4, 5]. In particular, it is suggested that the least aqueously altered parts are type 2.9 [4, 5], resulting in Paris to be considered as among the most pristine meteorites. Paris being a CM chondrite, its aqueous alteration is the main secondary process that has been considered, while its thermal history has been mostly overlooked. In the present work, by combining several analytical techniques on sub-samples of Paris, our objectives are twofold: (i) assess, through independent tracers, aqueous and thermal alteration of the Paris meteorite at the millimeter scale; and (ii) further refine our understanding of reflectance spectra of such materials. Reflectance spectroscopy is one of the main tool to characterize asteroids and to establish genetic links with meteorites. However, the interpretation of some spectral bands in terms of composition is not necessarily straightforward. We are here particularly interested in the mineralogical control of the so-called 0.7-micron band used as a proxy for hydrated minerals on asteroids [e.g., 6] and that is sometimes observed and sometimes not on Ryugu [e.g., 7], the asteroidal target of Hayabusa-2.”
