Yes, jno, 'coronate' is odd and appears to be unique to the US. However, it must have been used in England at one time. The OED gives 'coronate' as (first recorded in) Late Middle English! Coronate has come straight from Latin coronare and is formed from the past participle (coronatus).'Crown' has come to us by a less direct route, also from Latin ('corona' a wreath, a chaplet,) but via Old French and Anglo-Norman words. Crown got here first (it's 's Middle English).
Bet the Americans didn't know any of that and simply re-created the word as a back-formation from 'coronation' when the need arose for their press to describe a coronation LOL