Geologic Mapping C Question Marathon

[elephantower]

Nope, not a dome--for one thing domes are usually map-scale, not specimen-scale. It's a type of fold.
For the second one, I'm not even sure it's solvable--I'm working on it now. However, a bluntness of 1 means it's circular, not isoclinal (isoclinality is related to tightness, not bluntness).

[Pupitre]

Good news: Someone else answered a geomaps question!
Bad news: It was syo_astro...not exactly a new face in Geologic Mapping

Pupitre, you read a random article and came up with a tangentially related question? You wanna play that way? OK then:

Describe the relationship between cooling speed and columnar jointing shape in igneous lava flows. If you get that question without using google, I will personally bow down to you at nats...

So do you want me to tell you the other answers? Also, do you mind telling me how you figured out the intrado/extrado question? I want to see if we have the same thought process (and I'm a bit suspicious after your guessing comment).

Oh I missed this one. Well if you're looking for a formula, I'm sorry I'm at a loss. But columnar jointing, let me say, is probably one of the most badass rock formations to ever come into existence. Isn't cooling speed inversely proportional to the size of the columns created? At least that's what seems to make sense to me.

EDIT: Haha I had a feeling I was wrong in the first one. Now to consult my binder. Don't have that exact picture but my best guess is a sheath fold?

[elephantower]

Giant's causeway! Basically, fast-cooling flows joint pentagonally, and slow-cooling ones hexagonally. Also, yes, a sheath fold.

[Pupitre]

Giant's causeway! Basically, fast-cooling flows joint pentagonally, and slow-cooling ones hexagonally. Also, yes, a sheath fold.

Oh phooey...

1. What is a nappe and what are two landforms that can be created by nappe movement? Explain how each one is formed.

2. Relative to the hinge, what is the direction of slip in flexural-slip folding?

[elephantower]

That second question is solvable, and I just solved it

Here's how (Click to Show Hidden Text)

First, note that the bluntness=1. This means that it is a circular fold. Because it is concentric, the layers all have the same thickness. The borehole at the inflection points cuts along the diameter of the circle. Because there are 3 layers on each side of the axial plane, there are 6 layers cut overall. Thus, the thickness of each layer is 1000/6. Now, we need to find the chord formed by the intersection of the surface with the circle. To do this, use the formula for a chord 2*(r^2-d^2)^.5, where r is the radius of the circle and d is the perpendicular distance from the chord to the center. D is 2*1000/6=1000/3, and r is 1000/2=500. Then, to find the distance of the road, we use the formula sec(a)*c, where a is the angle between the line perpendicular to the exposed surface and the road, and c is the chord length. The answer is 1763.66 meters.

Your questions:

... (Click to Show Hidden Text)

1. Klippes and fensters? Low ridges? I'm not sure.
2. Awesome question: If the hinge is N then the slip is NE on the right side and NW on the left side of the axis.

[Pupitre]

That second question is solvable, and I just solved it

Here's how (Click to Show Hidden Text)

First, note that the bluntness=1. This means that it is a circular fold. Because it is concentric, the layers all have the same thickness. The borehole at the inflection points cuts along the diameter of the circle. Because there are 3 layers on each side of the axial plane, there are 6 layers cut overall. Thus, the thickness of each layer is 1000/6. Now, we need to find the chord formed by the intersection of the surface with the circle. To do this, use the formula for a chord 2*(r^2-d^2)^.5, where r is the radius of the circle and d is the perpendicular distance from the chord to the center. D is 2*1000/6=1000/3, and r is 1000/2=500. Then, to find the distance of the road, we use the formula sec(a)*c, where a is the angle between the line perpendicular to the exposed surface and the road, and c is the chord length. The answer is 1763.66 meters.

Your questions:

... (Click to Show Hidden Text)

1. Klippes and fensters? Low ridges? I'm not sure.
2. Awesome question: If the hinge is N then the slip is NE on the right side and NW on the left side of the axis.

Yep but you didn't explain what a nappe is A nappe is essentially when the hangingwall of a thrust fault moves more than 2 km from its original position. When a nappe moves, sometimes erosion loosens connecting portions in the sheet, creating a hole where a portion kind of falls out of the nappe. That is a klippen. A fenster any hole in a nappe where other rock crops or just nothing exists. For question 2, I was just looking for perpendicular but that's according to my source so I'm curious to hear where you learned that.

[elephantower]

Perpendicular? That sounds realllly suspect--what would that even mean when the layers are clearly not perpendicular to the hinge? The only exception is at the hinge point, but there is also no slip at the hinge-point. Basically, flexural slip is like folding a phone-book--look at the slip of the pages ( it isn't horizontal). To quote wikipedia "flexural slip allows folding by creating layer-parallel slip between the layers of the folded strata". Nowhere except the hinge zone are layers perpendicular to the hinge, thus layer parallel slip is not slip perpendicular to the hinge.
A helpful image:


Bonus Q:

What is a schuppen structure?

[elephantower]

So you seem to like domes and basins:

Eons ago, in a land far, far away, undeformed strata underwent folding in a small area. A few eons later, the whole region underwent folding again (but no faulting has occured in the area). The strata in the small area originally deformed now form dome-and-basin structures. What is the angle between the axial planes of the first set of folds and the second set of folds (outside of the originally deformed region)?

[Pupitre]

Perpendicular? That sounds realllly suspect--what would that even mean when the layers are clearly not perpendicular to the hinge? The only exception is at the hinge point, but there is also no slip at the hinge-point. Basically, flexural slip is like folding a phone-book--look at the slip of the pages ( it isn't horizontal). To quote wikipedia "flexural slip allows folding by creating layer-parallel slip between the layers of the folded strata". Nowhere except the hinge zone are layers perpendicular to the hinge, thus layer parallel slip is not slip perpendicular to the hinge.
A helpful image:


Bonus Q:

What is a schuppen structure?

Hm well that lecture power point I was looking at must have been wrong then. A schuppen structure is the same as an imbricate structure/fan right? It's when a series of branching reverse faults terminate at the same point.

[elephantower]

Yup! Can you link the source about slip? I'd definitely be inclined to trust a university lecture over my rambling...