Continental drift of a planet over 900 million years

Question

Over the past 2 weeks, I've been attempting to create a planet with a plausible continental drift. I was really hoping to get some kind of response to my work.

I'll stick up my hand and admit it right now - I am no expert on this matter. I've done a fair amount of research, but I have gaping holes in the field of geology.

One other thing, I apologise beforehand if this isn't the typical thing that is present on WSE. I've only seen questions posted here before, but I just thought I'd try my luck.

Anyway, without further ado, let's begin

900 MYA

Supercontinent, comparatively recent formation. Gradually drifting northwest.

800 MYA

Supercontinent continued, rift soon to form in the east.

700 MYA

Supercontinent has rifted, a larger portion in the west, a smaller portion to the east, hereafter referred to as Supercontinent A and Supercontinent B, respectively.

600 MYA

A narrow portion of land on the other side of Supercontinent A has rifted away, and what is left is about to rift in half very soon.

500 MYA

Supercontinent A has split entirely. The first portion to rift is moving north at a remarkably fast pace, and the remainder has split into a continent over the south pole, and a continent on the equator.

Supercontinent B has remained relatively stable, but this is not to last.

400 MYA

Supercontinent A's remnant on the equator moves northeast, and begins subduct the ocean to its eastern side, eventually including the rift of the original supercontinent

Supercontinent B rifts, and its western portion begins to be affected by the subduction, drifting westwards.

The continent over the south pole has also split in two, its more northerly portion set to collide with the continents upon the equator. Similar to the above-mentioned continent, it begins to subduct the rift present.

The narrow continent has split, one half on the equator, the other half having drifted farther north. Due to the subduction of the oceanic rift, however, the continent begins to drift back south.

300 MYA

Another supercontinent is due to form.

Supercontinent A's equator remnant has split, one half due to remain an isolated continent, for now.

200 MYA

A new supercontinent has formed, drifting north and rotating counter-clockwise. The isolated continent is drifting over the north pole, and a collision is due in several million years.

100 MYA

Isolated continent has collided, but the supercontinent itself is beginning to break up. A small island continent has split off.

Present

Supercontinent has split, two continents to the south, with a large island, and three continents to the north, one over the north pole.

EDIT - in response to an inquiry, a few details about the world itself, at least those that I've already figured out -

• Planet age - ~8.4B years
• Distance from star - ~3/4 Earth distance

So, yeah. Would love any responses. What is plausible, or not. If this is too open-ended, or opinion-based, I'll be perfectly happy to have this question closed. But yeah, responses are appreciated.

Answer 1

My first thought is that you are thinking too linearly. You've made a projection map of your planet onto a flat plane, and that is causing my some consternation. For instance, the 700MYA and 600MYA pictures show a continent in the middle of the ocean, moving apparently in a straight line. I am not sure how I feel about it, but my first thought is that it should be following more of a curve. The tectonic plates live literally on the surface of a sphere, so they will need to follow that sphere. Also remember that as one plate moves another gets pushed out of the way. so at 600 MYA you appear to have the central continent moving East but another moving West. This again sort of bothers me, but a big grain of salt here is that I am no geologist...

Answer 2

Plate tectonics of that style are a transient thing. Let's take earth at an example, where they started some way through the Archean eon, and are expected to come to an end up to 1 billion years from now because the mantle has cooled down so that subducting oceanic crust will get stuck. Continents are more complicated since they float on the denser mantle material, erode, fold up, are lifted and subside and so on.

On Mars, oth, this style of tectonics have never fully developed and tectonic activity came to an end much earlier in its history, or let's say took a very different course. Marsian surface can be bilions of years old, while oceanic crust on earth doesn't get older than ~200million years.

A planet of your envisioned age of 8.4 billion years and in the size range would long have cooled down and it's surface would have had ~3 billion years to erode and become less featured than that of a planet with active plate tectonics.

But, in principle and if you just wave the energy flux away (it's world building after all), a "supercontinent cycle" these days on earth takes somewere between 300 and 500 million years. That's roughly the time span for continents to breaks up, drift apart, and close again. This is called a "Wilson cycle", driven by density differences of cooling oceanic crust, and up to 3 of these would fit into your time span under current earthly conditions, making the envisioned changes principally plausible to me.