Target of bomb: pulverised zone, with rock sent skywards (6,4)
I believe the answer is:
ground zero
'target of bomb' is the definition.
(area struck by a bomb)
'pulverised zone with rock sent skywards' is the wordplay.
'pulverised' becomes 'ground' (past tense of 'grind').
'zone' becomes 'z'.
'with' is a charade indicator (letters next to each other).
'rock' becomes 'ore' (ores are found in rocks).
'sent skywards' says the letters should be written backwards (in a down clue, letters go up).
'ore' reversed gives 'ero'.
'ground'+'z'+'ero'='GROUND ZERO'
(Another definition for ground zero that I've seen is " brand new start".)