Shock a mate unnamed in US region (10)
I believe the answer is:
appalachia
'unnamed in us region' is the definition.
'appalachia' can be an answer for 'region' (I have seen 'American region' mean 'appalachia' so perhaps 'region' could also mean 'appalachia'). I am not certain of the 'unnamed in us' bit.
'shock a mate' is the wordplay.
'shock' becomes 'appal' (synonyms).
'mate' becomes 'chia' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'appal'+'a'+'chia'='APPALACHIA'
Can you help me to learn more?
(Other definitions for appalachia that I've seen before include "US mining area" , "American region" , "Mountainous region of eastern USA" , "US mountain region" , "Area of eastern US" .)