The dome looks papery and a bit torn. Do you see anything coming or going into the dome?
We think that this was the beginning of a nest made by social wasps. The nests aren't made of leaves but of a papery substance that the insects make from wood and saliva, and are placed up in trees/shrubs/overhangs etc.. 
It may have been torn apart somehow (wildlife/) before it really got going- look up- there may be more of it up high in an overhanging tree. (They generally won't bother you unless you directly threaten the nest).
Here is our page on social wasps:
https://extension.umd.edu/resource/social-wasps-yellowjackets-hornets-and-paper-wasps/


Christine