Hot answers tagged

4

We know the density of the core from seismology. We also know the density of pure iron at given pressure (P) and temperature (T). From these two, people have long noticed that there is a discrepancy: the actual core is lighter than a theoretical core made of pure iron. This is known as the Core Density Deficit (CDD). To explain this CDD, we need to add light ...


1

Iceland isn't only situated on a divergent boundary (which in itself can rise up to shallow depths because of higher static and dynamic lift btw.) but also on a (postulated) pretty deep rooted mantle plume that may produce enough magma to rise to subaerial heights. Edit: The magma that erupts at an ocean ridge is "welded" to the sides ("sheeted dykes"). ...


1

The reason islands don't form along divergent plate boundaries is that these boundaries are at the bottom of the sea, and usually quite deep. Although mid ocean ridges are volcanic, the magma doesn't get a chance to pile up and reach the surface because the plates are not static. They are slowly spreading apart, and the magma is needed to form fresh oceanic ...


1

This is a bedding plane, once horizontal, but geological forces have tilted it to the diagonal. The strata above have been eroded and washed into the sea, perhaps by a storm, leaving the ancient bedding plane exposed. Tilted strata are not unusual in very ancient rock formations.


1

New(ish) work on the matter: https://www.nature.com/articles/s41598-018-33823-y tl,dr: "Modern style" plate tectonics may be (at least) as old as 2.2Gy, probably having started 2.5Gy. Expanding as requested: The paper is not paywalled. It is about a metamorphic (by temperature and pressure altered) rock that fits in a regime that is typically connected to ...


Only top voted, non community-wiki answers of a minimum length are eligible