Ever since the plate tectonic paradigm-shift of the 1960s, geologists have strived to understand ancient rocks in terms of the movements of plates. The geology of north-western Ireland can be explained by what happened when a subduction zone ran out of oceanic crust back in the Ordovician. Let me take you back to before that… Continue reading The Grampian / Taconic orogeny in Ireland – when arcs attack
Category: metamorphism
How to make a rock from scratch
“If you wish to make an apple pie from scratch, you must first invent the universe.” Carl Sagan. I have a handsome piece of rock in my hand. How did it come to be, how was it made? A perfectly acceptable geological answer is that it formed as molten rock cooled slowly underground. But that’s… Continue reading How to make a rock from scratch
Eclogites: back to the surface
Eclogites are beautiful rocks that form deep within subduction zones. The vast majority of subducted oceanic crust becomes more dense than the surrounding mantle rocks and travels to the strange world of the deep earth. Lucky for us, small volumes make it back to the surface. How does this happen? As so often in the… Continue reading Eclogites: back to the surface
Oceanic crust – down to the core
Almost all of what I write about in this blog concerns only 1% of the earth’s volume. All crust, all sedimentary rocks, the glories of mountain building, all occupy an insignificant portion of the earth. It’s the only bit we can get to – in geology, we are the 1%. This post is all about… Continue reading Oceanic crust – down to the core