Robin's maid like some NW Pacific islands? (8)

I believe the answer is:

marianas

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'some nw pacific islands?' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'robin's maid like' is the wordplay.
'robin's maid' becomes 'marian' (I can't justify this - if you can you should give a lot more credence to this answer).
'like' becomes 'as'.
'marian'+'as'='MARIANAS'

Can you help me to learn more?

(Another definition for marianas that I've seen is " Pacific group".)

I've seen this clue in the Sydney Morning Herald.

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