combine european and american hops?

Are there any styles that use both American hops and European noble hops?

Most styles can use either or, or any combination. Most anything that is called "American" will generally be a bit stronger, and use AMERICAN style hops. Most things that are called English, will be a bit maltier or use a European hop.

Otherwise, use what taste good to you. If you are brewing for competition, read the style guide to know if there is a particular flavor the judges will be looking for.

I do a Belgian IPA with Saaz, Cascade/Amarillo, Magnum or CTZ.

SNPA uses Magnum, Pearle, and Cascades