[jhanschoo]

What, then, causes the phenomenon that fields interact with particles?

Historically, there has been a multitude of ideas and phenomena that have been labeled as causation. Aristotle, back then, identified four notions of causation, and the modern reader immediately will feel that some of these notions themselves are still too general. When you make a claim like "nature obeys causality", you need to be more precise in what you refer to by nature and causality, else your claim is far too ill-defined to mean much of anyting.