Migrating a tablespace to a different database on the same ASM
Transportable tablespaces and asmcmd cp command should do the trick.


Prepare transportable tablespaces metadata set.
Copy expdp file to location accessible by impdp from destination database.
asmcmd cp datafiles to new location.
Import TT metadata set.


If your ASM diskgroup uses some storage device with several disks then you should be able to improve performance by copying several datafiles in parallel.