If one thing sparks another, the first thing causes the second thing to start happening. What was it that sparked your interest in motoring? a row sparked by a comment about his sister. = cause Spark off means the same as spark. That incident sparked it off His book, Animal Liberation, sparked off a revolution in the way we think about animals. see also bright spark
If a burning object or electricity sparks a fire, it causes a fire. A dropped cigarette may have sparked the fire. = start