If I select Earth as my expanded element at level 7, do I gain the ability to manipulate metal, or is my ability to manipulate metal ONLY applied to the composite blast? I've yet to find any debate on this, which makes me wonder if this has been completely glossed over, or the answer is stupidly obvious. Either way, I don't know it, and would like to!
If your primary element is earth and you select earth as your expanded element then you have the prerequisites for the metal blast and receive it automatically. If you want to manipulate metal in other ways then that depends on which wild talents you have. The magnetism wild talent would help.