CAIs melting history

The chondrite parent bodies obviously could not have accreted before their constituent chondrules formed. Based on the formation times of chondrules, accretion of the ordinary chondrite parent bodies began 2.5-3 Myr after CAIs (4565.7—4565.2 Ma). The end of accretion can be inferred from the metamorphic history of the chondrite parent bodies. Isotopic data from metamorphic assemblages, coupled with thermal modeling of the chondrite parent bodies, suggest that the time of peak metamorphism for the H chondrite parent body was at-4563 Ma. As will be discussed in Chapter 11, it is likely that the source of heat for metamorphism on chondrite parent bodies was the decay of26 Al, perhaps with a contribution from 60Fe. Thermal evolution models indicate that accretion of chondritic asteroids could not have occurred earlier than -2 Myr after CAI formation, or they would have melted. 

Other components of chondrites such as AOAs (>90+ vol% forsterites), their cousins, and aggolmeratic chondrules have all experienced some level of melting, albeit very minor in most cases (Weisberg et al. 2003 Zanda et al. 2005). The reasons why AOAs were not melted extensively like chondrules and Type-B CAIs is unknown and no quantitative constraints on their thermal histories exist. 

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