Head deity's mantle encapsulating old belief (4,2,4,4)
I believe the answer is:
cape of good hope
'head' is the definition.
(I've seen this before)
'deity's mantle encapsulating old belief' is the wordplay.
I cannot quite see how this works, but
'mantle' could be 'cape' (synonyms) and 'cape' is present in the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found within the answer.
'belief' could be 'hope' (hope is a kind of belief) and 'hope' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cape of good hope that I've seen before include "Land's End?" , "Promising cover" , "head" .)