Rocky appearance of dated hairstyle (7)
I believe the answer is:
outcrop
'rocky appearance' is the definition.
'dated hairstyle' is the wordplay.
'dated' becomes 'out'.
'hairstyle' becomes 'crop' (I have seen 'Severe hairstyle ' mean 'crop' so perhaps 'hairstyle' could also mean 'crop').
'out'+'crop'='OUTCROP'
'of' acts as a link.
(Other definitions for outcrop that I've seen before include "Cop tour around projecting layer of rock" , "Rocky feature" , "Visible rock formation" , "Protruding or projecting rock" , "Jutting stone" .)