Great rift when cleric embraces heresy finally (6)

I believe the answer is:

canyon

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'great rift' is the definition.
'canyon' can be an answer for 'rift' (I have seen 'Big rift' mean 'canyon' so perhaps 'rift' could also mean 'canyon'). I'm not certain of the 'great' bit.

'cleric embraces heresy finally' is the wordplay.
'cleric' becomes 'canon' (I've seen this before).
'embraces' is an insertion indicator.
'finally' says to take the final letters.
The last letter of 'heresy' is 'y'.
'canon' going around 'y' is 'CANYON'.

'when' acts as a link.

Can you help me to learn more?

(Other definitions for canyon that I've seen before include "river valley" , "A deep gorge with a river, may be Grand" , "Deep, steep-sided valley" , "grand spectacle in Arizona" , "rift created" .)

I've seen this clue in The Guardian.

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