Constraining the alteration and metamorphic history of the CY-chondrite parent body with triple oxygen isotope analyses, and 53Mn-53Cr and U-Pb chronometry by utilizing the new Hyperion source at the Heidelberg Secondary Ion Microprobe Spectrometer core facility (HIP)

• Applicant: Privatdozent Dr. Jens Hopp
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 581871774

CY chondrites are a small group of carbonaceous CI-like chondrites, which more recently had been proposed to represent a distinct parent body sharing some properties with material collected from the Ryugu asteroid, and possibly Phaethon, the target asteroid of the planned JAXA Destiny+ mission. They differ from CI and CM chondrites in their mineralogy and their thermal history. Matrix in CY chondrites consists of anhydrous phyllosilicates indicative of higher retrograde peak metamorphic temperatures, and the proportion of Fe-sulfides distributed as small grains in the matrix is larger compared to other carbonaceous chondrites. Differences in their thermal history between some of the CY chondrites led to definition of two subgroups CY1 and CY2, the latter containing primary and secondary olivine and showing outlines of relict recrystallized chondrules and refractory inclusions, whereas the CY1 chondrites only display secondary olivine and are less thermally altered. Recent reports on differences in Cr and Ti isotope compositions between both subgroups raise the possibility of two independent carbonaceous parent bodies. CY1 chondrites contain periclase, significant magnetite and larger dolomite and apatite grains. Whereas the texture of CY1 chondrites is rather featureless, relict chondrules in CY2 are easy to recognize. Olivine in CY2 span a composition from large forsterite grains to mostly smaller Fe-rich olivine (Fo40-80). Oxygen isotopic composition is the heaviest among all meteorite groups and only surpassed by Ryugu carbonates. Thus, the CY parent body (or bodies) must have suffered a multi-stage fluid-driven hydrothermal alteration history that led to successive formation of dolomite and magnetite. In addition, thermal reheating also likely shifted the oxygen isotope composition towards higher values. No clear knowledge exists about the timeline of these alteration and metamorphic processes. The only 53Mn-53Cr age of dolomite in CY1 chondrite Y-980115 of 4563.8+1.2/-1.5 Ma indicates a rather prolonged time of fluid-mobilization. Reconstruction of various stages of fluid activity requires an age frame. For this purpose determination of U-Pb ages of apatite and Mn-Cr ages of dolomite and magnetite with ion probe analyses is proposed. Magnetite in CY1 chondrites shows two populations with one group containing few wt% Mn associated with Mn-bearing dolomite. Magnetite embedded in the matrix has low Mn. Triple oxygen isotope analyses of both magnetite suites and dolomites shall characterize the fluid regime during their formation. Triple oxygen isotope analyses of primary and secondary olivine shall trace retrograde metamorphic processes in CY2 chondrites. This study will enhance our understanding of the relative order of fluid reaction processes associated with hydrothermal alteration and thermal events, and further elucidate the nature of the reacting fluids.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr. Mario Trieloff; Dr. Alexander Varychev