The development of New Zealand as we know it today, began in the Carboniferous.
It was during this time that a subduction zone formed as the ancestral Pacific Ocean was thrust under the
western edge of Gondwana. The resulting string of volcanic islands,as well as
the thrusting up of scraped sediment from the ocean floor, are what New Zealand
was in it's earliest days. A deep trench was also formed in the process.
Much sediment was accumulated from neighboring Australia, Tasmania, and
Antarctica. This sediment filled up the trench and built around the string of islands