when u do the export, the table is exported with its existing defintions . so tables are exported with tablespace = system tablespace.
you have granted resource and dba role to the new user.
which give him right to write into any tablespace.
so, when importing, by default it import into system tablespace( read from the exported definitions).
you have do this.
1. create a new user(targetuser) and make new_tablespace as his 
    defualt tablespace;
2. do the import like following

   imp dba/password fromuser=sourceUser touser=targetuser file=somefile.dmp

-- since now, the defualt tablespace for target user
is not system tablespace, import will import into his defualt tablespace. 
-- again if there are any indexes in other tablespaces
it will be copied over to same tablespaces again beucase u have given the role resource.

and if you just trying to move the tables from the system tablespace ( the still owned by the same user)
try this

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alte table table_name move tablespace < your_new_tablespace >;