Physical Geology 101

16. Metamorphic Rocks II (p. 233-242)

Causes of Metamorphism

The two main processes that occur within a rock during metamorphism are:

 ______: physical processes like squeezing and crushing - caused by strong forces (causes a ______)

 ______: changes in mineral chemistry / growth of new minerals from old ones.

Can these two processes occur together at the same time? YES or NO

The six main driving mechanisms (types of metamorphism) for the above metamorphic processes are:

 ______metamorphism (aka ______metamorphism)  ______metamorphism  ______metamorphism  ______metamorphism  ______metamorphism (aka ______metamorphism)  ______metamorphism along fault zones

1. Contact or Thermal Metamorphism

Contact metamorphism occurs around an ______.

The heat of the intrusion radiates out and metamorphoses the rocks in contact with the intrusion, called host rocks or ______.

The region of metamorphosed rock around an intrusion is called an ______.

Contact metamorphism occurs around all types of igneous intrusions, regardless of their size. Examples: ______

Effect of intrusion size:

The larger the intrusion, the wider the zone of metamorphism around the intrusion. Batholiths can metamorphose rocks over a distance of ______away from the batholith. Dikes and sills may only have aureoles ______wide.

What other three factors may influence the size of an aureole?

1. ______2. ______3. ______

1 Physical Geology 101

Which type of magma produces the widest aureoles, and why?

Type: ______Reason: ______

Temperature is more of a factor than pressure around an intrusion. So which type of metamorphic process is most commonly associated with contact metamorphism?

mechanical deformation OR mineral recrystallization?

So contact metamorphosed rocks usually don't have a foliation.

Typical metamorphic rock type produced: ______

2. Hydrothermal Metamorphism

Many of the hot fluids, or ______, coming off of a magma intrusion can cause changes in the minerals in the surrounding rocks. This is called hydrothermal alteration.

This type of metamorphism, driven by fluids, is also called ______.

Environment where metasomatism commonly occurs: ______Types of minerals that form here due to hydrothermal alteration: ______, ______, and ______

Hydrothermal fluids may also carry metallic ions that precipitate valuable ore minerals in the rocks around the intrusion. What are nine examples of these ore minerals?

1. ______2. ______3. ______4. ______5. ______6. ______7. ______8. ______9. ______

3. Regional Metamorphism

How large of an area may be affected by regional metamorphism?

______

Regional metamorphism occurs at convergent plate boundaries where tectonic plates collide. What are two characteristics of these types of locations?

1. ______2. ______

The resultant metamorphic rocks form the deep cores of the mountains (e.g., the ______). The rocks are highly deformed and foliated, which tells us that strong forces must have been involved in their creation.

So which type of metamorphic process is most commonly associated with regional metamorphism?

2 Physical Geology 101

mechanical deformation OR mineral recrystallization?

What types of metamorphic rocks are associated with regional metamorphism?

______

4. Burial Metamorphism

Burial metamorphism occurs in regions where a lot of sedimentary rocks get piled on top of each other inside a so-called ______. The rocks get buried deeper and deeper under the weight of the rocks on top. These basins can extend down to depths of ______km.

Initially the sediment undergoes diagenesis, turning the sediment into rock. Then, when the rocks get buried to depths where the temperature exceeds ______C, burial metamorphism begins.

Typically, the metamorphic rocks so produced do not exhibit a foliation. So which type of metamorphic process is most commonly associated with burial metamorphism?

mechanical deformation or mineral recrystallization?

5. Dynamic Metamorphism in Fault Zones

What does dynamic mean? ______

This type of metamorphism results predominantly from large differential stresses within narrow zones of deformation in the crust called fault zones or ______.

Near the surface, the deformation in fault zones is brittle and results in a highly fragmented rock called fault breccia. Deeper down, where temperatures are higher, minerals recrystallize and get aligned parallel to each other, producing a noticeable foliation. The type of fault rock produced is called ______.

What minerals are common in these rocks? ______and ______.

Based on the strongly foliated rocks, which type of metamorphic process is most commonly associated with dynamic metamorphism?

mechanical deformation OR mineral recrystallization?

6. Impact or Shock Metamorphism

This type of metamorphism is produced by the instantaneous spike in heat and pressure caused by the collision of a rapidly moving projectile with the Earth.

These projectiles are called ______. The types of impact-produced rocks that are created are called ______.

Mineral Assemblages and Metamorphic Grade

What are the three grades of metamorphism?

3 Physical Geology 101

______, ______and ______

Where contact metamorphism occurs around an igneous intrusion, the grade of metamorphism ______as you get further and further away from the intrusion. This makes sense because the rock temperature gradually gets less and less further away from the intrusion so the metamorphic grade must decrease.

We see this change in metamorphic grade by the different combinations of metamorphic minerals present in the rocks. Any particular combination of minerals is called a: ______

At different distances from an intrusion, different combinations of minerals can be seen, even though the original rock was the same at each point before metamorphism began. Each mineral assemblage is characteristic of specific metamorphic conditions (grades).

Are the types of minerals that occur in each assemblage dependent on the type of rock being metamorphosed? YES or NO ?

Geologists have studied metamorphic rocks in great detail and have determined that specific assemblages of minerals occur consistently when any particular rock type gets metamorphosed. These mineral combinations are called: ______

Example: if a clay-rich rock (e.g., shale) gets metamorphosed, the resultant rock contains the minerals muscovite and chlorite. What do these minerals indicate about the grade of metamorphism? (choose one)

Low grade Intermediate grade High grade

If muscovite and chlorite start to turn into the mineral biotite, what is the grade of metamorphism? (choose one)

Low grade Intermediate grade High grade

If we have a metamorphosed clay-rich rock that contains the minerals garnet, staurolite, or sillimanite, what is the grade of metamorphism? (choose one)

Low grade Intermediate grade High grade

For the same original rock type (like shale), the index minerals are always the same for a particular metamorphic grade. This is why mineral assemblages in metamorphic rocks can tell us so much about the conditions of metamorphism.

Do we see the same index minerals as in clay-rich rocks when we progressively metamorphose basalt to higher and higher metamorphic grades?

YES or NO ?

We know exactly which mineral assemblages result from the metamorphism of specific rock types, so we can always determine the grade of metamorphism by identifying the index minerals present in the rock.

4 Physical Geology 101

What do we call lines on a geologic map that show the boundaries between the locations of different grades of metamorphic rocks with different mineral assemblages?

______

Pressure and Temperature Ranges of Metamorphic Conditions

The full range of temperature and pressure conditions that control the grade of metamorphism for any rock type can be divided up into a number of smaller divisions of discrete T and P ranges called ______.

Metamorphic facies are just a more refined way of looking at metamorphic grade.

FINAL QUESTION:

What are the different types of metamorphic facies?

______