According to the law of cross-cutting relationships, in a geological feature where an igneous rock body is intruded by any intrusive body such as a fault and d(i)kes, then the intrusive bodies are considered to be younger than the surrounding igneous rock.
In the given condition, the basalt is the older surrounding rock which is being cut across by a fault, and this follows the principle of cross-cutting relationship.
If you're referring to streams/rivers of water that run independently of another source in the ocean these are referred to as "currents" and can be very powerful depending on their location.
