- Forms in fractures of rocks already in place, so it an INTRUSIVE feature
- Form at right angles to the direction of extension in the area - nature’s frac jobs
- Can be super thin or super thick, but generally are self-consistent
- Can have multiple periods of injection or even multiple compositions of injection over time
- Can get en echelon patterns, rings, and cones (last two common with caldera volcanism)
- Magmatic are the most well known and form when magma flows into a crack and cools into a sheet.
- The igneous rock is generally more weathering resistant so we get cool weathering features
- Can be rhyolitic, but mostly basaltic
- Rate of cooling determines grainsize (slow = big) and big near the center
- Can have columnar jointing
- Big phenocrysts orient with flow direction - cool! AMS studies show this.
- These are awesome when you get them radially around a volcano!
- Horizontal dikes are called sills
- Clastic dikes are formed by sediments episode 177
- Can be formed with fluid pressure
- Cracks in permafrost that fill in
Fun Paper Friday
- One plus one equals two, right? Sure, but you won't get published saying it that way.
- Siegfried, John J. "A first lesson in econometrics." Journal of Political Economy 78.6 (1970): 1378-1379.