Exploring the Variability of Primitive Materials and Processes in the Early Solar System: Characterisation of Four Chondritic Meteorites

Primitive asteroids provide unique clues about the astrophysical and geological processes that occurred at the birth of the solar system ~4.56 billion years ago. Primitive asteroids are thus targets of several national and international space missions (Dawn, OSIRIS REx, Hayabusa II) and sample returns from these bodies are under intense cosmochemical investigation in a major international complementary effort. Within this framework, I have petrographically (and spectroscopically) characterized four new primitive chondrites from Antarctica with two specific objectives: i) to complete and publish their classification in the Meteoritical Bulletin Database of the Meteoritical Society; ii) to highlight unusual features for further in-depth investigations that will expand our knowledge on the aqueous alteration processes in primitive asteroids and the geological context for the formation of extraterrestrial organics. The four meteorites studied in this work are Reckling Peak (RKP) 17043, 17075, 17085 and Elephant Moraine (EET) 14079. They were recently collected (in 2017 and 2014) by the Italian Programma Nazionale delle Ricerche in Antartide (PNRA). Polished thin sections were investigated by means of optical microscopy (transmitted and reflected light), Raman Spectroscopy and microanalytical Field Emission Gun Scanning Electron Microscopy (FEG-SEM-EDS) at the Dipartimento di Scienze della Terra and Centro per la Integrazione della Strumentazione dell’Università di Pisa (CISUP), Italy. In addition to my analytical work, I conducted X-ray mapping tests to generate high-quality compositional maps in relatively short acquisition times in order to maximize the analytical potential of the CISUP FEG-SEM-EDS laboratory (see Appendix). Based on petrographic analyses RKP 17043, 17075, 17085 and EET 14079 are classified as an L3 ordinary chondrite, a CM1 and a CM2 Mighei-type carbonaceous chondrites and a CV3 Vigarano-type carbonaceous chondrite, respectively. The diversity of the chondrites studied allowed to highlight similarities and differences between chondrites belonging to different classes (ordinary versus carbonaceous chondrites), groups (CM and CV carbonaceous chondrites) and petrologic types, as reflection of different geologic processes on different parent asteroids. The following are examples of remarkable features that would require further detailed studies: i) aqueous alteration fronts as key features for investigating pathways for fluid/element mobilization on CM hydrous/icy parent asteroids (RKP 17085), (ii) unusual mineral assemblages in chondrule pseudomorphs dominated by sulfide-carbonate-rich phases as ground for expanding our knowledge on aqueous alteration reactions and conditions (RKP 17075), (iii) melt inclusions held within olivine crystals in the CM2 chondrite RKP 17085 that could provide insights into chondrule formation processes. Finally, my Master thesis work comprised the on-line publication of the Atlas of Meteorites in Thin Sections, an educational tool for students interested in the petrography and petrology of planetary materials. The atlas is a collection of 123 microphotographs of a wide spectrum of thin stony meteorites from the collection of the Museo Nazionale dell'Antartide in Siena, Italy