The old, unique C1 chondrite Flensburg – Insight into the first processes of aqueous alteration, brecciation, and the diversity of water-bearing parent bodies and lithologies

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Bischoff, A., Alexander, C., Barrat, J., Burkhardt, C., Busemann, H., Degering, D., Di Rocco, T., Fischer, M., Fockenberg, T., Foustoukos, D., Gattacceca, J., Godinho, J., Harries, D., Heinlein, D., Hellmann, J., Hertkorn, N., Holm, A., Jull, A., Kerraouch, I., King, A., Kleine, T., Koll, D., Lachner, J., Ludwig, T., Merchel, S., Mertens, C., Morino, P., Neumann, W., Pack, A., Patzek, M., Pavetich, S., Reitze, M., Rüfenacht, M., Rugel, G., Schmidt, C., Schmitt-Kopplin, P., Schönbächler, M., Trieloff, M., Wallner, A., Wimmer, K., Wölfer, E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Tagish; Tagish Lake
• Online Access: http://hdl.handle.net/21.11116/0000-0007-8521-D

On September 12, 2019 at 12:49:48 (UT) a bolide was observed by hundreds of eye-witnesses from the Netherlands, Germany, Belgium, Denmark and the UK. One day later a small meteorite stone was found by accident in Flensburg. The presence of short-lived cosmogenic radionuclides with half-lives as short as 16 days proves the recent exposure of the found object to cosmic rays in space linking it clearly to the bolide event. An exceptionally short exposure time of ∼5000 years was determined. The 24.5 g stone has a fresh black fusion crust, a low density of <2 g/cm3, and a magnetic susceptibility of logχ = 4.35 (χ in 10 −9 m 3 /kg). The rock consists of relict chondrules and clusters of sulfide and magnetite grains set in a fine-grained matrix. The most abundant phases are phyllosilicates. Carbonates (∼3.9 vol.%) occur as calcites, dolomites, and a Na-rich phase. The relict chondrules (often surrounded by sulfide laths) are free of anhydrous silicates and contain abundant serpentine. Lithic clasts are also surrounded by similar sulfide laths partly intergrown with carbonates. 53 Mn- 53 Cr ages of carbonates in Flensburg indicate that brecciation and contemporaneous formation of the pyrrhotite-carbonate intergrowths by hydrothermal activities occurred no later than 4564.6 ± 1.0 Ma (using the angrite D'Orbigny as the Mn-Cr age anchor). This corresponds to 2.6 ± 1.0 or 3.4 ± 1.0 Ma after formation of CAIs, depending on the exact absolute age of CAIs. This is the oldest dated evidence for brecciation and carbonate formation, which likely occurred during parent body growth and incipient heating due to decay of 26 Al. In the three oxygen isotope diagram, Flensburg plots at the 16 O-rich end of the CM chondrite field and in the transition field to CV-CK-CR chondrites. The mass-dependent Te isotopic composition of Flensburg is slightly different from mean CM chondrites and is most similar to those of the ungrouped C2 chondrite Tagish Lake. On the other hand, 50 Ti and 54 Cr isotope anomalies indicate that Flensburg is ...