Week 5 - David Clark - Convergent Plate Boundaries - New Zealand

This Winter, I had a trip planned to New Zealand. Now with the coronavirus, I am not sure if that trip is still on. Suffice to say, it has been on my mind lately! So this week I wanted to visit New Zealand academically to see what kind of plate activity is going on there. I know that they experience a very high volume of earthquakes, and recently had a volcanic eruption. What is going on to drive these geological processes?! It turns out, quite a bit geological activity is happening in New Zealand.

First off, New Zealand straddles two plates, the Australian and the Pacific. But what I found so interesting is that one plate isn't submerging below the other along this line. What is happening under the North Island of New Zealand is the Pacific Plate is being subducted under the Australian plate in a normal fault. Then, about 1,000 miles to the South, under the South Island, the Australian plate is being subducted under the Pacific plate in a reverse fault zone! Oh don't worry, there is more geological activity going on. Between theses subduction zones, the plates are sliding past each other in a strike-slip fault, which is really a transform fault because it is "accommodating motion between two tectonic plates" (Lutgens & Tarbuck, 2016). Below is a good diagram of what is happening:

Obviously this massive amount of plate activity is the cause for the earthquakes in New Zealand. Whether along the subduction zones or the Alpine fault (transform fault), there is plenty of plate compressional activity happening. But wait, that's not all! Also along the North subduction zone, where the Pacific is subducting under the Australian plate, the Australian plate is under tensional stress, and it is thinning. This thinning of the plate, in combination with the subduction, is letting water and magma join together and rise, creating volcanic activity. In fact, New Zealand is a volcanic hot zone!

About 26 million years ago, volcanoes started erupted in and around New Zealand, creating new land as the volcanoes erupted. In geologically terms, this is pretty recent. For the last 26 million years, the volcanoes kept erupting, further expanding the New Zealand land mass. Obviously, this means New Zealand is composed of tons of volcanic minerals, but also contains oceanic minerals as well! Why's that? Well, apparently New Zealand may actually be part of a continent called Zealandia that is mostly submerged (geosociety.org):

Whether or not it ends up being categorized as a continental plate or not, this "continent-like" land mass exudes all the characteristics of a continental plate, except most of it's area is submerged. This brings me to my final point, that historically, New Zealand is exhibiting an oceanic to oceanic plate boundary convergence. I know for the assignment we were supposed to be focused on continent plate boundaries, but once I started researching this I couldn't stop! Also, depending on your thoughts from the article published on geosociety.org, this may actually be a continent plate boundary!





References:

Lutgens, F. K., & Tarbuck, E. J. (2016). Essentials of geology (13th ed.). Upper Saddle River, NJ: Prentice Hall.
 
https://www.geosociety.org/gsatoday/archive/27/3/article/GSATG321A.1.htm