A couple of possibilities here to backup archived logs out of ASM to File System, and then cleanup the ASM diskgroup of archives already backed up.
What I'm doing in some cases is to move archived logs out to file system, from there they are moved by a backup application to a backup server and to tape.
This Script : Cleanarch backup archived logs out of ASM to File System, It does this in 2 groups:
Group #1 all archived logs until 12 hours before, are backed up and removed from ASM
Group #2 all archived logs between 12 hours before and the time of the last archived sequence are also backed up but they are kept on ASM.
The until time can be easily changed:
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