At www.nature.com/news/geology-north-america-s-broken-heart-1.14281 … apparently, a huge rift valley cleaved N America down the middle, one billion years ago – and then failed. Why?
At the border of Minnesota with Wisconsin, the St Croix River runs along part of the ancient rift, a beauty spot with high basalt cliffs on one side of the water. These are volcanic rocks in what is a geological puzzle. Rifts are thought to grow and eventually break apart – all part of the Plate Tectonics consensus theory. The rifts eventually become a new sea, or ocean. This is how the Atlantic is thought to have been formed, along the volcanically active Mid Atlantic Ridge, with the plates being pushed aside, millimetre by millimetre, eventually forming the ocean as it now is.
Why didn't it happen with the above rift? The crack in the earth was 3000km in length – but never came to anything. It didn't grow wider, it didn't leak water, it didn't do anything. It was and is just a rift in the crust of the earth – somewhat akin to the modern Rift Valley across Africa and the Levant.
The rift is now mostly buried under sediments many feet thick but one wonders what this means for the modern Rift Valley. Will it really open up and form a new continental land mass, causing a split in Africa. Indeed, does it shine an unwelcome light on Plate Tectonics theory?
Donald Patten thought the Great Rift Valley was formed by the Earth changing its axis of rotation, providing the stress to crack the crust.