To create or clone a new partition in a MDS repository look into the following documentation
http://download.oracle.com/docs/cd/E14571_01/core.1111/e10105/repos.htm#CIHIDABJ

13.3.6.1 Cloning a Partition

In many cases you might want to group the soa composites so that it is easy to identify the required composite.
The best way to do this is to create a new partition and deploy the related soa composites to this partiton.

By default , if you don't speciy the partition name, all the composites are deployed to the "default" partition.

This blog shows how to create a new partition using the oracle fusion middleware enterprise manager console.

1.  Log into the em console
2.  Expand the SOA node  on the Left hand side navigation pane.
3.  Select the "soa-infra (server name)" node .
4.  On the Righthand side select the "soa-infrastructure"  related menu and select the menu "Manage Partitions"
5.  Now Create a new partition using the "create" icon.