Experimental Investigation of Core Formation in the CV-CK Chondrite Parent Body

Several recent studies have proposed that the carbonaceous chondrites of Vigarano (CV) and Karoonda (CK) groups share a common parent body that was partially differentiated with an interior core dynamo. The CK chondrites are metamorphosed at higher temperatures than CV chondrites, and would represent the more interior portions of the unmelted chondritic layers of their parent body. Therefore, CK chondrites should be the closest analog materials to those that underwent partial melting to form an interior core. CK chondrites are among the most oxidized among chondrite groups and do not contain metallic FeNi, which raises the question, if their parent body had a core dynamo, what would its core be composed of? In this work, we are conducting partial melting experiments at pressures relevant for the interiors of planetesimals (e.g., 50 MPa) on CK chondrites to investigate the possible composition and mineralogy of the core of the hypothesized CV-CK chondrite parent body. In a preliminary experiment at 1100 °C and buffered by Co-CoO, we partially melted homogenized CK chondrite powder (LEW 87009) in a vertical cold seal furnace with a molybdenum alloy pressure vessel equipped with rapid in situ quench system. We observe that potential core forming material is primarily magnetite with only a very minor sulfide component and no metal. The magnetite in this experiment consistently co-exists with the silicate liquid, frequently with a vermicular texture. The magnetite ( 5 g/cm³) could ultimately separate from the silicate liquid (3.0 g/cm³) by density. However, the experiment is modally dominated by olivine ( Fo₆₀, 3.6 g/cm³). If the magnetite physically separated downward through residual mantle olivine, it could form a magnetite core but would not be likely to drive a dynamo. A core dynamo on the CV-CK chondrite parent body, if it existed, would require a much more complex thermal and redox structure than previously hypothesized for planetesimals in the early Solar System.