Share
Explore BrainMass

Explore BrainMass

Differential Stress

What can result from differential stress other than flat rocks and what ways does water play a role in the metamorphic process?

Solution This solution is FREE courtesy of BrainMass!

Please see response below. I also attached an excellent resource on metamorphism, including diagrams for illustrative purposes.

RESPONSE:

1. What can result from differential stress other than flat rocks?

Definitions:

Stress: is the force acted on per unit of surface area, SI unit = Newton/m2=Pascal.

Uniform stress: is a condition in which the stress is equal in all.

Differential stress: is when stress is not equal in all directions. When these forces come from differential stress, it causes rocks to either stretch, squeeze or cause slippage and translation depending on the kind of differential stress that occurs.

For example, there are three kinds of differential stress, which have different results:

1. Tensional Stress: Stretches Rocks
2. Compressional Stress: Squeezes rocks
3. Shear Stress: Causes slippage and translation (http://www.gl.ntu.edu.tw/file/course/gst4_9.ppt).

In fact, tectonics forces continuously squeeze, stretch, bend, and break rock in the lithosphere. The source of energy is the Earth's heat, which is transformed into to mechanical energy (http://www.gl.ntu.edu.tw/file/course/gst4_9.ppt).

2. What ways does water play a role in the metamorphic process?

Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means "change in form", derived from the Greek words meta, "change", and morphe, "form". The protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound physical and/or chemical change. The protolith (pre-existing rock) may be sedimentary rock, igneous rock or another older metamorphic rock.

Water plays a role in metamorphism.

1. Transports chemical involved in metamorphism

For example, metasomatism is the drastic change in the bulk chemical composition of a rock that often occurs during the process of metamorphism. It is due to the introduction of chemicals from other surrounding rocks. Water may transport these chemicals rapidly over great distances. Because of the role played by water, metamorphic rocks generally contain many elements that were absent from the original rock, and lack some that were originally present. Still, the introduction of new chemicals is not necessary for re-crystallization to occur (http://en.allexperts.com/q/Geology-1359/Sedimentory-metamorphic-rocks.htm)

2. Role in hydrothermal metamorphism

Hydrothermal metamorphism is the result of the interaction of a rock with a high-temperature fluid of variable composition. The difference in composition between existing rock and the invading fluid triggers a set of metamorphic and metasomatic reactions. The hydrothermal fluid may be magmatic (originate in an intruding magma), circulating groundwater, or ocean water. Convective circulation of water in the ocean floor basalts produces extensive hydrothermal metamorphism adjacent to spreading centers and other submarine volcanic areas. The pattern of this hydrothermal alteration is used as a guide in the search for deposits of valuable metal ores. (Also see more on hydrothermal metamorphism in the attached resource)

This is not exhaustive, but touches on the main points.

BEST OF LUCK!

Attachments