Presumably the desk top is no longer attached to its base, so no match is required, unless there is a base that is made of a different material or materials. If it happens that the top has an existing base in the same material and an existing finish it would normally make sense to refinish the top with the same finish as the base.
Anyway, assuming the top doesn't need to match anything else, I'd avoid a finishing oils which, as a group, tend to be a bit soft and relatively easily damaged. Imbuia is quite pale so an oil based interior varnish (short oil type) would be a tough and durable option with the characteristic of ambering or darkening the wood which helps bring out its character. Oil based varnishes have instructions for cleaning application tools (brushes, etc) with white spirits, or similar.
You could also use a water borne varnish (brush cleaning guidance is soap and water) but these can sometimes look a bit cold or lifeless and don't change the underlying wood colour as much as oil (solvent) varnish.
Personally, I'd go with the oil based interior varnish.
However, if you have spray equipment, you don't say but I guess that's not the case, that opens you up to a host of alternative finishes. Slainte.