Grade 10 - Geology - LO.6 - Metamorphic rock

   

We have in LO.6 Geology G10

First: the Concepts

A) Changes in temperature, pressure, or composition in Earth's subsurface can change the texture

and mineral composition of pre-existing rocks, creating metamorphic rocks.

B) Deformation during metamorphism produces foliated textures and may destroy original textures.

C) Deformation (change in shape) and stresses (distribution of forces) are related, but maximum

deformation and maximum stress are not always parallel.

D) The metamorphic texture and mineralogy observed in metamorphic rocks are most commonly

related to the conditions when the rock experienced its maximum temperature.

Second: the References

Earth comm: Ch.3 sec.4

Third: the Videos links

Fourth: Skills

A) Identifying and differentiating slate, phyllite, schist, gneiss, hornfels, marble, and quartzite in

hand specimens and outcrops according to texture and mineral composition.

B) Using microscopic scale features to interpret and classify different types of metamorphic rocks.

C) Using metamorphic rock texture to infer the presence or absence of deformation at the time of

metamorphism

D) Interpreting geological maps that describe the geology of Egypt.

Fifth: the materials as PPT., DOCX., and PDF

In the Drive from this link

Few Notes:

In the Investigate, you looked at what properties geologists use to classify metamorphic rocks. You then classified several samples. You also simulated how rocks change their shape, or deform, during metamorphosis. Finally, you used a geologic map to locate metamorphic rocks in your local area and region. Sedimentary and igneous rocks can be turned into metamorphic rocks. To do so, they need to be subjected to high temperatures and/or pressures. The process is called metamorphism. The changes occur while the rock is still solid. The temperature of the rock is not so high that part of the rock melts. If the temperature becomes too high, part of the rock melts to form magma. The magma later cools to form an igneous rock.

Crystals of a mineral can grow only in a certain range of temperature and pressure. Suppose a mineral crystal in a rock is subjected to the high temperatures and pressures outside of this range. Metamorphosis occurs. The mineral crystal is changed into crystals of one or more different minerals. This is why the minerals in a metamorphic rock are usually very different from the minerals in the original rock. However, a few common minerals, such as quartz and calcite, do not change form. When a limestone is metamorphosed, the calcite continues to exist. However, the crystals grow to be much larger. All evidence of the original features of the limestone is destroyed. For example, there is no more evidence of fossils.

Geologists have learned a lot about metamorphic rocks in labs. They use special furnaces. These furnaces can be heated to extremely high temperatures. They are also under tremendous pressure. These are the temperatures and pressures under which metamorphic rocks can form. Using these studies, the geologist can infer the temperatures and pressures in Earth when the rocks were formed. Recall that every rock “tells a story.” Metamorphic rocks have their own story to tell.

The temperature of a rock can be increased in two ways. Rocks can be buried deeper and deeper in Earth. This can happen by deposition of a very thick layer of sediment on top of the rock. It can also happen by movement along faults. Very thick masses of rock are shoved on top of the rock. As the rock is buried, its temperature gradually increases. This is because the temperature in Earth increases with depth. Enormous volumes of rock can be metamorphosed in this way by deep burial. This is the most important kind of metamorphism. It is called regional metamorphism, because large regions of Earth’s crust can be affected in this way.

The temperature of a rock can also be increased if a body of magma passes near the rock. As the magma cools, the surrounding rock is heated. This can metamorphose the rock. If the intrusion is small, only a thin layer of the surrounding rock is metamorphosed. However, very large intrusions can metamorphose a large amount of rock. Surrounding rock for thousands of meters away from the intrusion can be changed. The further away from the intrusion, the less the degree of metamorphism.

Deformation in Metamorphism

Extreme deformation is common during regional metamorphism. In Part B of the Investigate, you modeled the deformation of a rock by shearing. The same thing happens, usually even more so, when rock is sheared by forces within Earth. This is especially common where one lithospheric plate slides down beneath another. You saw in the Investigate that when a material is sheared, lines or planes within it become more parallel. This is called transposition. In many metamorphic rocks, all kinds of features and structures are “smeared out” by transposition to become nearly parallel planes. The layering you see in a metamorphic rock may not have anything to do with layering in the original rock. Forces within Earth can also stretch or compress the rock. In some metamorphosed conglomerates, the pebbles are stretched into a shape similar to a test tube.

Foliation in Metamorphic Rocks

Some sedimentary rocks contain a high percentage of very fine flakes of mica minerals. These include claystone, mudstone, and shale. These rocks become metamorphosed first to slate. Then they become phyllite, and then schist. It depends on the intensity of metamorphism. You looked at the classification table in the Investigate. You noticed that all of these rocks tend to split easily along parallel planes. This is because the mica minerals in the rock have grown to be parallel to one another. This causes weakness in the direction parallel to the planes of the mineral grains. The parallel growth develops for two reasons. First, the mica minerals grow with their planes perpendicular to the direction of greatest force on the rock. Second, when the rock is sheared, the mica grains tend to become parallel, as you read earlier. The tendency for a metamorphic rock to split along parallel planes is called foliation. Foliation,  is a major feature of many metamorphic rocks

We are glad for you to utilize our site. We furnish you with the assistance of introducing information to you as Egypt's extraordinary understudies in STEM Schools. This assistance is given from the data of master instructors and contemporary extraordinary understudies, and you can likewise help us in that by sharing your data, whatever it is through the WhatsApp and Telegram groups,  which will You can discover them on the Home page of the site.💪Good Luck