Stunned, noting a mature reasoning (13)

I believe the answer is:

argumentation

'reasoning' is the definition.
(argumentation is a kind of reasoning)

'stunned noting a mature' is the wordplay.
'stunned' is an anagram indicator.
'noting'+'a'+'mature'='notingamature'
'notingamature' is an anagram of 'ARGUMENTATION'.

I've seen this clue in The Telegraph.

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