Calcium-aluminum-rich inclusions recycled during formation of porphyritic chondrules from CH carbonaceous chondrites

We conclude that CH porphyritic chondrules formed by incomplete melting of isotopically diverse solid precursors, including mineralogically and isotopically unique CAIs commonly observed only in CH chondrites. Therefore, the CH porphyritic chondrules must have formed in a distinct disk region, where the CH CAIs were present at the time of chondrule formation. Because most CH CAIs avoided chondrule melting, we infer that chondrule formation was highly localized. These observations preclude formation of CH porphyritic chondrules by splashing of molten planetesimals, by impact processing of differentiated planetesimals, and by large scale nebular shocks, e.g., shocks driven by disk gravitational instabilities or by X-ray flares. Instead, they are consistent with small-scale chondrule-forming mechanisms proposed in the literature, such as nebular processing of dust balls by bow shocks and by current sheets.