Aqueous alteration of kamacite in CM chondrites

摘要: Abstract– The study of aqueous alteration kamacite in CM chondrites provides insight on the conditions, products, and relative timing alteration. We studied unaltered, partially altered, fully altered grains from Murray, Murchison, Cold Bokkeveld, Nogoya using optical microscopy, electron microprobe analysis, scanning Raman spectroscopy. From textual evidence chemical we established three separate microchemical environments. 1) In a environment with high S activity, alters to form tochilinite, P-bearing sulfides, eskolaite, schreibersite. Mass balance calculations show that 81% Fe is removed region, making it available for formation other minerals or Fe-rich aureoles. release can alter mesostasis type-I chondrules forming cronstedtite. 2) Si activity low cronstedtite small accessory sulfide inclusions. 3) A limited results magnetite. resulting magnetite retains associated Ni distinguish precipitated addition, phases pentlandite apatite be formed if Ca are present. Finally, note tochilinite matrix lack typical Ni, P, Co levels, suggesting they did not but possibly by sulfidization