elaboration vs expanding upon

elaboration and expanding upon both are nouns.

Word	Noun	Adjective	Verb	Adverb
elaboration	Yes	No	No	No
expanding upon	Yes	No	No	No

As nouns, expanding upon is a hypernym of elaboration; that is, expanding upon is a word with a broader meaning than elaboration:

elaboration: addition of extra material or illustration or clarifying detail
expanding upon: adding information or detail

Other hypernyms of elaboration include expansion.

elaboration (noun)	expanding upon (noun)
developing in intricate and painstaking detail	adding information or detail
addition of extra material or illustration or clarifying detail
marked by elaborately complex detail
a discussion that provides additional information
the result of improving something