Petrology, trace element abundances and oxygen isotopic compositions of a compound CAI–chondrule object from Allende

摘要: Abstract We report the petrology, trace element abundances and oxygen isotopic characteristics of a compound CAI–chondrule object, WI-025, found in Allende CV3 chondrite. The WI-025 is an irregularly shaped inclusion consisting three texturally chemically distinct portions: interior portion, igneous rim intermediate zone located between these two portions. portion consists anorthite, spinel, olivine Al-bearing low-Ca pyroxene. major chemistry corresponds to that Al-rich chondrules character fine-grained spinel-rich CAIs ferromagnesian chondrules. has abundant 16 O-rich spinel (Δ 17 O = −14.2 −24.7) displays group II CAI-like REE composition. These observations indicate contains CAI component formed by fractional condensation. had subsequently assimilated chondrule materials through partial melting. maximum heating temperature melting estimated at approximately 1400 °C, similar Type-B CAIs. compositions pyroxene O = −6.3) assimilation took place under moderately O-poor nebular gas. entirely surrounds portion. are indistinguishable from those pyroxenes. material, which was melted same gas as accreted represents reaction accompanying formation. formation history can be summarized following processes: (1) original formation, (2) assimilation, (3) (4) secondary alteration on parent body.