Deformation and Metamorphism
1. Explain the difference between load pressure and directed pressure, using diagrams.
Directed Pressure
Load Pressure
Load pressure refers to when underlying rock has equal pressure exerted on it from all sides. However, directed pressure is when there is not equal forces pressing on the rock from all directions and lateral forces which cause compression and buckling of rocks.
a) What observable differences are there between rocks affected by load pressure and directed pressure?
Texture, size and shape are all things which change when a rock is subjected to directed pressure. Directed pressure caused grains to become distorted and then recrystallise to finer grained granular aggregates. A rock which has been subjected to directed pressure is also likely to be elongated into a different shape.
b) Describe three textures that result from directed pressure
Slaty Cleavage is foliation in very fine-grained rocks which results from directed pressure and the parallel alignment of microscopic mica flakes. This property is what causes the rock to be easily split apart.
Lineation is also caused by directed pressure to rocks. This texture results from the parallelism of prismatic minerals and is why it resembles a bunch of pencils.
Layering is another metamorphic structure which might result from directed pressure. Instead of the minerals being evenly distributed throughout the rock; certain minerals are concentrated in layers. This structure is common in rocks called gneiss and is called a gneiss structure.
The Term Paper on Igneous Rock
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2012) Geologic provinces of the world (USGS) Shield Platform Orogen Basin Large igneous province Extended crust Oceanic crust: 0–20 Ma 20–65 Ma >65 Ma Igneous rock (derived from the Latin word ignis ...
2. Explain with diagrams the difference between a horst and a graben.
A Graben is a long, narrow trough which is bounded by one or more parallel normal faults. A horst is the opposite; it is a ridge which is most commonly caused my normal parallel faults.
3. Name and discuss the four main factors which cause metamorphism
Heat and Pressure: Heat and pressure work simultaneously to begin the process of metamorphism. Heat increases with depth and respectively so does the pressure exerted on underlying rocks. Heating a rock makes the atoms in the minerals vibrate and become more mobile. Eventually the minerals break up and produce new minerals.
Fluids: Diffusion occurs through mineral grains but mainly along the boundaries and minute fractures of the rock. Diffusion is the atoms within the rock beginning to slowly move around. Small amounts of pore fluids, mostly water, greatly assist in this transfer of atoms.
Time: Time is the final factor which is necessary for metamorphism to take place. These small scale processes produce remarkable end products if given an enormous period of time to occur.
4. Describe the metamorphic changes resulting from the intrusion of a large igneous batholith.
a) What is this form of metamorphism called?
This is called Thermal metamorphism because it is caused by heat acting as a single metamorphic agent.
b) Use a diagram to show the contact aureole and how different country rocks are affected by the intrusive rock.
PINK: Limestone
GREEN: Shale
BLUE: Sandstone
BLACK: Granite Intrusion
RED: Aureole
c) Explain what factors determine the width of the aureole
There are 3 main factors which affect the width of the aureole in thermal metamorphism. The first factor is the size of the igneous body. The second factor is the temperature of the igneous body and the third factor relating to the width of the aureole is the rock it’s intruding into. Heat will travel much quicker through a porous rock such as limestone compared to other rocks.
The Term Paper on Sedimentary Rock 2
Sedimentary rock formation begins with igneous, metamorphic, or other sedimentary rocks. When these rocks are exposed at the earth’s surface they begin the long slow but relentless process of becoming sedimentary rock. Weathering All rocks are subject to weathering. Weathering is anything that breaks the rocks into smaller pieces or sediments. This can happen by the forces of like wind, rain, and ...
5. Complete the following block diagrams and identify each structure.
SEE SHEET
6. Name each geological structure
a) Tilted bedding
b) Graded bedding
c) Plunging fold
d) ???
Copyright N.B.B, 2010
