Download Background Information for Plate Tectonics Rock Formation

Background Information for
Plate Tectonics & Rock Formation
Background concepts needed to achieve objectives.

Basic understanding of the Earth’s Interior
1. Crust: made up of oceanic crust (basalt – dense) & continental crust (granite
– less dense than basalt), solid
2. Mantle – made up of three parts. Lithosphere (solid, floats on asthenosphere).
Asthenosphere (soft material that can slowly flow). Outer mantle (solid).
3. Core – Outer Core (liquid metal). Inner Core (Solid metal).
4. Temperature & Pressure increase as you go towards the center of the Earth

Heat Transfer & Convection
1. Heat is always transferred from a warmer substance to a cooler substance
2. Convection is heat transfer by the movement of a heated fluid. It is caused by
differences in temperature and density within the fluid. Warmer materials are
less dense because the molecules move faster and spread apart. Cooler
materials are more dense because the molecules move slower and are closer
together. Gravity pull the more dense materials down and the less dense
materials rise.
3. A convection current is the flow that transfers heat within a fluid. In the
Earth’s Mantle the Asthenosphere flows. The heat from the Earth’s core heats
up the lower asthenosphere. This materials becomes less dense than the
material above it and it starts to rise. Gravity pulls the cooler material down
towards the core. Because the lower mantle and lithosphere are solid the
asthenosphere continuously flows up and down.
4. These convection currents inside the asthenosphere cause the lithosphere to
move. This movement allows the continents to drift. Continental Drift is the
hypothesis that all continents had once been joined together in a single
landmass know as Pangaea.

Sea-Floor Spreading
1. Ocean thermal vents are places in the Ocean floor where ocean water sinks
through cracks, or vents, into the crust. This water is heated by contact with
hot material from the mantle and then spurts back into the ocean. In these
areas where there is no light and where temperatures would normally be
freezing there is tons of life living around theses vents.
2. Mid-Ocean Ridge is the longest chain of mountains in the world. This ridge
extends into all of the Earth’s oceans. At the mid-ocean ridge, molten material
rises from the mantle and erupts. The molten material then spreads out,
pushing older rock to both sides of the ridge.
3. Sea-Floor Spreading is the process that continually adds new material to the
ocean floor at the mid-ocean ridge. As new material is added the old rock
moves aside in both directions.
4. Deep-ocean Trenches are underwater canyons where the oceanic crust bends
downwards and is pushed back into the mantle. Without the existence of these
trenches the ocean floor would continuously increase because of sea-floor
spreading.
5. Subduction is the process by which the ocean floor sinks through a deepocean trench and back into the mantle. The ocean floor near a deep ocean
trench is cooler and more dense than the ocean floor at the mid-ocean ridge.
This more dense material is heavier and over tens of millions of years will
sink back into the mantle at the trenches.

Plate Tectonics
1. Plate Tectonics is the geological theory that states that pieces of the Earth’s
crust are in constant, slow motion, driven by convection currents in the
mantle. As the plates move, they collide, pull apart, or grind past each other,
producing volcanoes, earthquakes, mountain ranges and deep-sea trenches.
2. There are three types of plate boundaries.
a. Transform Boundary. Here plates slide past one another moving in
opposite directions. No crust is created or destroyed. Earthquakes are
common here.
b. Divergent Boundary. A place where two plates move apart. Most
occur at the mid-ocean ridge. On land a deep valley called a rift valley
is formed.
c. Convergent Boundary. A place where two plates come together. The
density of the plates decides what happens. When oceanic crust
collides with oceanic crust or continental crust the more dense material
will sink below the other into a deep-ocean trench. Volcanoes are
common here. When continental crust collides with continental crust
the less dense granite squeeze into mountain ranges.

Minerals
1. A mineral is a naturally occurring, inorganic solid that has a crystal structure
and a definite chemical composition. There are over 3,000 minerals. About 20
of these minerals make up most of the rocks of the Earth’s crust.
a. Inorganic: means that the mineral cannot arise from materials that
were once part of a living thing.
b. Crystal structure: particles in a mineral line up in a unique pattern that
repeats over and over again. It has flat sides that meet at sharp edges
and corners.
c. Chemical composition: a mineral always contains the same elements
in the same proportions.
2. Identifying minerals.
a. Hardness: A mineral can scratch any mineral softer than itself, but
will be scratched by any mineral that is harder. Compare to Mohs
Hardness Scale.
b. Color.
c. Streak: the color of its powder. This can be observed by rubbing a
mineral against a piece of unglazed tile.
d. Luster: how a mineral reflects light from its surface. Terms to
describe luster include: bright, metallic, shiny, glassy, earthy, waxy
and pearly.
e. Density: the mass in a given space. Dividing the samples mass by its
volume gives the density of the mineral.
f. Crystal Shape: Look at the number and angle of the crystal faces.
These can be classified into six groups.
g. Cleavage and Fracture: the way a mineral breaks. Cleavage is a
mineral splits easily along flat surfaces. Fracture describes how a
mineral looks when it breaks. Some terms to identify fracture include:
shell-shapes, hackly (jagged), earthy (crumble easily), and uneven
(rough, irregular surfaces).
h. Special properties: Some glow (fluorescence), magnetic, radioactive,
react to acid, electrical, etc.
3. Minerals can be formed in two ways:
a. Crystallization of melted materials: As hot magma cools inside the
crust or as lava hardens on the surface. The size of the crystals depends
on the rate at which the magma cools, the amount of gas it contained,
and the chemical composition of the magma. Magma deep below the
surface cools slowly and forms large crystals, magma towards the
surface or lava on the surface cools quickly and forms smaller crystals.
b. Crystallization of materials dissolved in water: Magma can heat
water causing minerals to dissolve inside it producing a solution. A
solution is a mixture in which one substance dissolves inside another.
When the hot water solution begins to cool minerals are left behind.
Many minerals form from solutions at places where tectonic plates
spread apart along the mid-ocean ridge and at ocean thermal vents.
c. Minerals formed by evaporation: Minerals can form when solutions
evaporate. Ex. Several minerals form from the evaporation of seawater
(halite, gypsum, calcite, and minerals containing potassium)
4. Minerals are the source of metals, gemstones, and other materials used to
make many products.
a. Gemstones: rubies & saphires
b. Metals: aluminum, iron, copper, silver
c. Other uses: foods, medicines, fertilizers, and building materials. Ex.
Talc is made into talcum powder, Flourite is used to make aluminum
& steel, Calcite is used in microscopes, Quartz is used to make glass,
watches & electronic equipment, Kaolin is used to make high-quality
china &pottery, Gypsum is used to make wallboard, cement & stucco,
Corundum is used in polishing & cleaning products.
d. Ore: a rock that contains a metal or economically useful mineral. Most
metals are not in pure form they are a combination of that metal &
other elements. Smelting is the process of removing a metal from an
ore. An alloy is a solid mixture of two or more metals.

Rocks
1. Rocks are made of mixtures of minerals and other materials.
2. Classifying Rocks:
a. Color
b. Texture: the look and feel of the rock’s surface (smooth & glassy,
rough or chalky). Most rocks are made up of particles of minerals or
other rocks, which geologists call grains.
 Grain Size: Large and easy to see are called coarse-grained.
Small enough to only be seen under a microscope are called
fine-grained.
 Grain Shape: They can look like tiny particles of sand,
seeds, exploding stars or they can be fragments of other rock
and be smooth and rounded or jagged.

Grain Pattern: Some lie in flat layers and look like a stack
of pancakes, others have a swirling pattern, some occur in
rows and others are random.
 No visable grain: Not even under a microscope. Rocks like
this cooled very quickly giving them a smooth, shiny texture
like glass.
c. Mineral Composition: By looking at a small sliver of a rock under a
microscope a geologist can observe the shape and size of the crystals
in the rock and identify the minerals. Mineral tests can also be used
such as Mohs hardness scale, acid test, and magnets.
3. Formation of rocks:
a. Igneous rock forms from the cooling of molten rock – either magma
below the surface or lava at the surface.
 Extrusive rocks formed from lava that erupted onto the
Earth’s surface. (Ex. Basalt) Rapid cooling lava forms finegrained rock with small crystals or glassy texture with no
visable crystals.
 Intrusive rocks formed when magma hardened below the
Earth’s surface. (Ex. Granite) Slow cooling magma forms
coarse-grained rock with large crystals.
 Uses: Most are hard, dense and durable. They have been used
for tools and building materials. Obsidian – tools, Granite –
buildings, bridges, paving streets, decorative stonework, Basalt
– crushed to make gravel used in construction, Pumice –
abrasive used for cleaning & polishing, Obsidian – heated to
form perlite which is used in place of soil for starting seeds.
b. Sedimentary rock forms when particles of other rocks or the remains
of plants and animals are pressed and cemented together. This rock
forms in layers below the surface.
 Forces such as heat, cold, rain, waves & grinding ice constantly
break up the Earth’s surface. Erosion is when running water,
wind or ice loosen and carry away fragments of rock.
 As the water or wind slows down is deposits its sediment. In
water these materials sink to the bottom of the ocean or lake.
Deposition is the process by which sediment settles out of the
water or wind carrying it. These deposits may include shells,
bones, leaves, stems, and other remains of living things.
 Compaction is the process that presses sediments together. As
more and more sediment falls on top, creating new layers, the
weight of the layers squeezes the sediments tightly together.
 During compaction minerals in the rock dissolve in water and
seep into the spaces between the particles of sediment.
Cementation is the process in which dissolved minerals
crystallize and glue particles of sediment together. This process
takes millions of years.
 There are three types of sedimentary rocks: Clastic, Organic
and Chemical. Clastic rocks forms when rock fragments are
squeezed together. Ex. Shale, sandstone, conglomerate &
breccia. Organic rocks form where the remains of plants and
animals are deposited in thick layers. Ex. Coal (remains of
swamp plants) & Limestone (produced from the hard shells of
living things). Chemical rock forms when minerals that are
dissolved in a solution crystallize (limestone) or from mineral
deposits left when seas or lakes evaporate (rock salt).
 Uses: Sandstone & Limestone have been used as building
materials or for decorating the outside walls of buildings.
Limestone is important in smelting iron ore and for making
cement.
c. Metamorphic rock is formed when an existing rock is changed by
heat, pressure, or chemical reactions. Most forms deep underground.
 Forms from collisions in the Earth’s plates where rock is
pushed down towards the heat of the mantle. Pockets of rising
magma can also produce metamorphic rock. Under pressure
minerals change into other minerals.
 Classified by the arrangement of the grains that make up the
rocks. Foliated means that the grains are arranged in parallel
layers or bands (Ex. Slate, schist & gneiss). Nonfoliated means
the mineral grains are arranged randomly (Ex. Marble &
quartzite).
 Uses: Marble is used for buildings & statues. Slate is used for
flooring, roofing, outdoor walkways or chalkboards.
4. Rock Cycle: Forces inside Earth and at the surface produce a rock cycle that
builds, destroys and changes rocks in the crust. Plate movements drive the
rock cycle by pushing rocks back into the mantle, where they melt and
become magma again. Plate movements also cause the folding, faulting, and
uplift of the crust that move rocks through the rock cycle. Subduction zones
and the collision of continental plates contribute to the rock cycle.
 Subducting Oceanic Plates: Sand that becomes sandstone as part of the
oceanic crust drifts towards a deep-ocean trench. As the trench, subduction
returns the sandstone to the mantle where is melts, forms magma and
eventually becomes igneous rock.
 Colliding Continental Plates: This process could squeeze sandstone from
the ocean floor resulting in a metamorphic rock, quartzite. This rock
eventually could end up at the top of a mountain range or plateau where it
will eventually erode away.