You could either use a Database Gateway for Oracle (Dg4ODBC or DG4TERADATA) or as an alternative use Oracle GoldenGate.
What is the requirement for 'freshness'?
As mentioned you can use the Gateways or Oracle GoldenGate, although Oracle GoldenGate capturing from Teradata is not that fast.
Another option might be ODI.
Is the 100gb of data to be moved in one piece, for example a complete table in one go, or is it smaller amounts of data over a period that add up to 100gb ?
This can have an influnece on the best method to set up the data move.
You could also use IRI NextForm (DB migration tool), or preferably its parent CoSort product (for the data movement speed) in that situation. Both share the same metadata and Eclipse GUI for the source-target connections between Teradata and Oracle. The data movement is either through ODBC, or bulk extract (from TD into flat files) then bulk pre-sorted loads into SQL*Loader, per: http://www.iri.com/blog/vldb-operations/high-speed-database-loading/