Geo Lab Midterm Powerpoints

• Crust:
– Continental Crust
– Oceanic Crust
• Mantle:
– Asthenosphere
– Upper mantle
– Lower mantle
• Core:
– Outer Core
– Inner Core

Lithosphere = Crust + uppermost
upper manlte

the
idea that the present-
day continents were
once part of a single
supercontinent

The
earth’s lithosphere is
broken into several
large rigid slabs called
plates, plates are
moving apart along the
mid-ocean ridges
continually.

Pacific
• North
American
• South
American
• African
• Eurasian
• Antarctic
• Indo-
Australian

Subduction Zones
– Volcanic Arcs
– Island Arcs
– Ocean-Ocean, Ocean-
Continent, Continent-
Continent

MOR (Mid Oceanic Ridge)
– Sea Floor Spreading
– Upwelling of Molten Material

Mostly made up of transform
faults (e.g. zones where rock
bodies slip past each other

Convergent
– Folding and Faulting: Uplift
– Reverse Faults /Thrust Faults
– Compression
• Divergent
– Thinning of the crust
– Subsidence
– Normal Faulting
– Tension due to spreading
– Upwelling of Molten Material
• Transform
– Strike Slip Fault or Transform Fault
– Slide past one another/shearing
– Formation of mini basins and ranges
• Complex Plate Boundaries also exist.
2010 Pearson Education, Inc.

• Paleo-climate belts
• Exact deposits of
continental glaciers
are found in near
equatorial Africa,
South America, and
India
• The fossil record
supports and gives
credence to the
theories of continental
drift and plate
tectonics

Earthquakes: Generated at the plate margins
• Paleomagnetism: Rocks that formed millions years ago
contain a “record” of the direction of the magnetic poles
at the times of their formation.
• Earth’s magnetic field reversed periodically.
• Recorded in minerals.
2010 Pearson Education, Inc.

Hot Spots:
• An area of unusual volcanic
activity
• Not associated with plate
boundaries
• Youngest at the hotspot
• cool -> dense -> subside ->
erosion -> Seamounts
• Volcanic islands created by
hotspots allow us to track
the rate and direction of
plate movement.
Plumes do not move!

Convection Cells-
• Drag and move the
lithospheric plates
Hot Spots-
• Injection of magma

The boundary between two plates that are moving away from each other is called a divergent boundary (Fig. 2.1C). The more common type of divergent boundary involves oceanic lithosphere along mid-ocean ridges. Partial melting of the asthenosphere below a mid-ocean ridge generates magma that rises in small blobs, eventually being transferred to a magma chamber in the lower oceanic crust. (Partial melting, as the name implies, does not involve the complete melting of the asthenospheric upper mantle, which remains mostly solid.) As the two plates move apart perpendicular to the ridge crest, also known as the ridge axis or axial rift, tension cracks develop along the axis that are filled in with magma.

A solid inorganic substance of natural occurrence

• Inorganic
• Naturally Occurring
• Solid
• Definite Crystalline Structure
• Definite Chemical Composition

Grouped by chemical
composition
• Major groups include:
– Native elements
(e.g., gold, diamond)
– Silicates
(e.g., olivine,
plagioclase,
mica, ...)
– Oxides
(e.g., quartz, hematite,
corundum, ...)
– Hydroxides
(e.g., goethite)
– Sulfides
(e.g., pyrite, ...)

Sulfates (e.g., barite)
– Carbonates (e.g., calcite, dolomite)
– Halides (e.g., halite, fluorite)
– Phosphates (e.g., apatite)

Shape
• Color
• Luster
• Hardness
• Streak
• Cleavage
• Texture
• Magnetism
• Specific Gravity
• Taste
• Odor
• Effervesces with HCl

Every mineral has a crystal form. The crystal form is the
shape that a crystal takes if it grows unimpeded.

mportant : Most mineral specimens are
irregular grains, very few display their
characteristic crystal habit.

Wavelengths of visible light are absorbed or
reflected by the mineral. Sometimes color is
determined by trace elements.
• Some minerals change color or have various
forms of different color
• You cannot rely on color when it comes to
mineral identification

Luster: a reflective property of mineral
surfaces.
• Usually we begin by separating the Metallic
and Non-Metallic minerals.
* Some minerals exhibit both metallic and non-
metallic properties.

There are two types of metallic minerals:
Metallic and Sub-Metallic.

Decreasing reflectivity:
Adamantine - Glassy/Vitreous - Resinous
• Other lusters
Pearly, Greasy/Oily, Silky, Dull, Earthy

Color of a powdered mineral which is tested by
rubbing the mineral across a porcelain streak
plate.

Cleavage: Tendency of
a mineral to break
along flat planes of
weaker bonding.
• Cleavage Planes 0+
Fracture: Cleavage is
absent and mineral
breaks irregularly

The ability of a mineral
to break or come apart
in a consistent way
• breakage is along
atomic planes
• cleavage is consistent
with crystal symmetry
and may be one to
multi-directional from
one mineral to
another.

Describes the inability
of a mineral to break in
a consistent way and
therefore not along
cleavage planes
Conchoidal- a smooth,
curved breakage in all
directions

Magnetism: Some minerals are magnetic. This
ranges from weakly to strongly magnetic.
Specific Gravity: The specific gravity of a material is
a comparison of its weight with the weight of an
equal volume of water. Specific gravity measures
the density of a material.
Taste: Some minerals exhibit a specific taste.
(i.e. Halite and Sylvite)
Odor
Effervesces with HCl: Fizz or give off bubbles.

A rock is a naturally occurring solid aggregate of
one or more minerals or mineraloids

Molten rock cools and Igneous rocks are
formed.
• Metamorphic rocks are formed when pre-
existing rocks are changed by temperatures
and pressures.
• When loose grains/sediments undergo
lithification, the result is a Sedimentary rock.

Rock Composition
– Grains, Clasts, Crystals
• Rock Texture: Description of the grains and
other parts of a rock: size, shape, arrangement
– Glassy, Fine to Coarse Grained, Vesicular,
Crystalline, Foliated, Clastic: can include fossils,
tracks, etc.
• Grain Size: Course, Medium, Fine
• Grain-shape: Round to AngularWeathered: fragmented into grains,
chemically decayed to residues, or even
dissolved.
• Eroded: worn away
• Sediment: an accumulation of chemical
residues and fragmented rocks, mineral
crystals, plants, or animals.
• Lithification: hardened (compaction and
cementation)

An igneous rock formed when magma or lava cools.

Based on where magma cools:
Intrusive Rocks: cool at
depth(magma). This means
that they cool at slower rates
and therefore have larger
crystals.
Extrusive Rocks: cool at the
surface(lava). This means that
they cool at faster rates and
have smaller crystals.

Based on magma composition
Ultramafic: rare, primitive,
mantle-derived
Mafic: (Mg, Fe)rich, more
dense, oceanic crust
Intermediate: mix of mafic
and felsic
Felsic: (Al, Si)rich, less
dense, continental crust
An igneous rock formed when magma or lava cools.

Almost entirely magnesium and
iron silicates (ferromagnesian
minerals)
• Minerals: olivine, pyroxene, Ca-
rich plagioclase
• Mafic mineral content: 86-100%
• Rarely observed on the Earth's
surface. Believed to be major
constituent of Earth's mantle.
Commonly found as xenoliths in
basaltic lavas.
• Rock types: peridotite/
pyroxenite, komatiite/picrite

Contains abundant
ferromagnesian minerals.
Usually dark in color.
• Minerals: olivine, pyroxene, Ca-
rich plagioclase, (amphibole)
• Mafic mineral content: 46-85%
• Characteristic of Earth's oceanic
crust; Also found on the Moon,
Mars, and Venus. Forms a runny
(low viscosity) lava
• Rock types: gabbro, basalt

Intermediate in composition between felsic and mafic
• Minerals: pyroxene, amphibole, plagioclase, biotite, quartz
• Mafic mineral content: 16-45%
• Rock types: diorite, andesite

• Dominated by silicon and aluminum (SiAl). Light color, characteristic
of continental crust. Forms a stiff (viscous) lava or magma.
• Minerals: K-feldspar, plagioclase, quartz, biotite, (amphibole).
• Mafic mineral content: 0-15%
• rock types: granite, rhyolite

• Mafic: Oceanic crust is created where at
  divergent boundaries. Hot spots also tend to
  be mafic.
  • Felsic: A magma chamber that pushes itself
  through a continental plate tends to be felsic
  • Intermediate: Volcanic Arcs

Common Structures of intrusive
igneous rocks:
Batholith = large intrusion of
magma
Sill = horizontal intrusion of
magma
Dike = vertical intrusion of magma
Volcanic Neck = core of volcano
(magma)
Common Structures of extrusive
igneous rocks:
Lava flows
Volcano cones (made of lava or
from pyroclastics)
Pyroclastic flows (made of
pyroclastics –ash, lapilli, and Volc.
Bombs)

Pegmatitic - very large crystals (many > 2 cm),
shows very slow cooling (plutonic)

Phaneritic - visible crystals, shows slow cooling,
usually 1-10mm. (plutonic)

Porphyritic – two distinct crystal sizes, large
ones and small ones. Generally due to a change
in the rate of cooling.

Aphanitic – crystals are too small (< 1mm) to
see, shows very fast cooling, (Volcanic i.e. from
lava).

Vesicular - Rock contains vesicles (gas bubbles trapped in
lava), which form from depressurization of the magma.
often looks like a sponge (usually Volcanic)

Glassy – looks like glass. Very rapid cooling
(quenching), forms volcanic glass, no crystals
present.

Pyroclastic texture – fragments of volcanic
glass, ash, cinders, Volcanic bombs

Phenocryst- A phenocryst is a relatively large and usually
conspicuous crystal distinctly larger than the grains of the
rock groundmass of a porphyritic igneous rock.
Xenolith- (Greek: "foreign rock") is a rock fragment
which becomes enveloped in a larger rock during the
latter's development and hardening.

Derives from the rapid cooling of a very viscous
magma of granitic composition; as a result it is
mainly found in domes, chimneys, dikes, and
more rarely in proper lava flows.
Generally Pyroclastic or Aphanitic

The friction and viscosity of the magma causes
phenocrysts and xenoliths within the magma or
lava to slow down near the interface and
become trapped in a viscous layer. This forms
laminar flow, which manifests as a banded,
streaky appearance.

Tuff- is a type of rock consisting of consolidated
volcanic ash ejected from vents during a
volcanic eruption.
Welded Tuff- The ash, pumice, and clasts were
so hot that they remelted to form a glassy rock
after landing on the ground. Most of the thin
clasts are pumice blocks that collapse and
flattened as they were reheated.

A rock formed from the accumulation and
consolidation of sediment, usually in layered
deposits.

A sedimentary rock is made up of GRAINS (rock
fragments, minerals, and fossils)
There are two types of sedimentary rocks:
Chemical (includes biochemical – sometimes
referred to as biogenic – and evaporites) and
Clastic (aka: Detrital).

Clastic Rocks are formed through 3 processes:
1. Weathering:
is the process of breaking down rocks and minerals
into smaller pieces by water, wind, and ice.
This creates the grains
2. Erosion (Transport) & Deposition:
Grains are transported by wind or water, variable
distances. Deposition occurs in various location and
is directly related to the energy of the environment.
3. Lithification:
the hardening of sediments through compaction and
cementation
This forms the rock.

Chemical Rocks are
formed through solution.
For Example:
Limestone: CaCO3
precipitates from a
solution to form rocks.
Chert: SiO2 precipitates
from a solution to form
what we call siliceous
oozes.

Rocks that form as a result of biologic processes -
i.e. rocks made of organic remains. These can be
unaltered, or diagenetically altered (altered after
formation) to varying degrees:
• Most calcium carbonates (limestone and
dolostone)
• Silicates (chert)
• Phosphatic rocks
• Plant remains (coal)
• Marine organics (oil shale and petroleum)

The grains of a sedimentary rock give us a
story of the origin of the grains & what type of
environment the rock formed in.
• 5 types of properties that we look for
1. Grain size
2. Grain shape
3. Sorting
4. Fossils
5. Chemical Properties

tells us how far the
grains traveled before deposition

The smaller the grain
size, the farther the
grain traveled.
Gravel: Grains > 2mm
Sand: Grain size ranges
between 1/16 mm to 2
mm
Silt: Falls between sand
& clay
Clay: Grains are too
small to see with the
eye or hand lens.

also tells us how far a
grain has traveled

Rounding - During transport, grains may be reduced in
size due to abrasion (rounding off of the sharp corners
and edges of grains). Rounding of grains gives us clues to
the amount of time a sediment has been in the
transportation cycle.
• Rounded = more travel time (lots of abrasion)
• Angular = less travel time (not as much abrasion)

tells us how far grain
traveled and energy level of transportation

Degree of uniformity of
grain size:
• Well Sorted:
– Grains are all the same size
– Low energy transportation
(i.e. slow river)
– Long travel time
• Poorly Sorted:
– Grains are different sizes
– High energy transportation
(i.e. debris slide, gravity flow)
– Short travel timed energy level of transportation

tell us environment of
deposition

Marine fossils (i.e. shells)
– Rock formed in marine environment
– i.e. Limestone
• Plant fragment fossils or terrestrial animal
fossils (i.e. tracks, bones)
– Rock formed on lands

Fizzes with HCL
– Is made of calcite, probably a limestone of some
sort
• Doesn’t fizz with HCL
– Is not made of calcite, probably some sort of
detrital rock
Things to watch out for:
Calcareous matrices (in detrital rocks!)

• Made up of rock fragments & minerals
• Grains have usually been transported some distance
• Examples: Sandstone, Conglomerate, Arkose
Sandstone, Breccia, Siltstone, Shale/Mudstone

Energy, rate of deposition, and the
environment: based on grains, clasts, and
matrices
• Mineralogy of the rocks tell us how far
sediment has travelled and the
environment it was deposited in.
• Matrix: Calcite, Hematite (red), Silica

Made up calcite in
the form of shells or
shell fragments
– Indicates marine
environment
– Organisms produce
calcite to form their
shells
• Fossiliferous
Limestone, Coquina

Form by chemical
precipitation in
evaporating pools of
water
– Grow in place
• Usually look
crystalline, but not
always
• Examples: Rock Salt
(Halite), Rock Gypsum

• Structures that form during or shortly after
  deposition of the sediment.
  Some sedimentary structures are created by the
  water or wind which moves the sediment.
  Other sedimentary structures form after
  deposition - such as footprint, worm trails,
  raindrop imprints or mudcracks

Each bed = interval of deposition of that sediment
• Each bedding plane = break in depositional cycle
• Beds usually accumulate horizontally (Law of Original
Horizontality)

Result of sediment being
transported and
deposited in one
direction by some
current
• Can be big or small
• Are relicts of
dunes/current ripples
• Can indicate desert ,
river, or beach
environments
• Can show paleocurrent
direction

indicates deposition above sea level on dry land,
exposed to atmosphere
• Mudcracks = dry environment
• Raindrops = that it rains (can really assume if area
is prone to heavy precipitation or not

A rock that has been altered in form due to heat,
pressure, and/or hydrothermally. Changes in form
include change in:
• Crystal Shape/size – this is called Recrystallization
• Rock/Mineral shape – high Temp allows rock to act
ductile , allowing rock to be deformed by high Pressure
• Mineralogy – different minerals can form in the rock
due to metamorphism.
• Metamorphic T & P are not high enough to melt a rock.
• Is derived from a protolith (aka A Parent Rock)
• Protoliths include Igneous, Sedimentary and even
Metamorphic rock types

• A measure of how much the
rock was metamorphosed.
• Slate is produced through
low grade metamorphism
• Gneiss is produced through
high grade metamorphism
• Slate was metamorphosed
at lower Temperatures (T)
and Pressures (P), while
Gneiss was metamorphosed
at higher T & P
Different metamorphic grades
produce different mineralogy
and textures (more on this later)

Regional Metamorphism:
• Occurs over large areas due to tectonic processes
• Pressure involved is moderate to high
• Temperature involved is low to high
• Associated with batholiths (only because these are associated
with regional tectonics), rock burial (subduction), folding,
mountain building, etc. caused by tectonics

Contact Metamorphism:
• Occurs locally, next to igneous intrusions, or from
hydrothermal fluids from intrusions
• Pressure is low to moderate
• Temperature is moderate to high

Metamorphic Names reflect chemistry and
texture (just like igneous rocks).
Two things you need to know in order to name a
rock:
1. Texture type
2. Mineral types present

There are two primary
types of metamorphic
textures.
1. Foliated
2. Non-Foliated

Foliation refers to the
layering and parallel
alignment of mineral crystals.
Foliation forms perpendicular
to pressure
4 types of foliation textures:
• Slaty cleavage
• Phyllite texture
• Schistosity
• Gneissic Banding

If it has slaty cleavage, it is Slate
• Slaty Cleavage refers to the way the rock breaks into
tabular sheets, roughly oblique to perpendicular in respect
to the foliated crystals (usually mica)
• No visible mica grains
• Slate usually does not have a sheen to it (though may have
a dull sheen) – why would it have no to dull sheen?
• Represents low grade metamorphism

No visible mica grains
• Glossy/bright sheen
• Wavy to wrinkled foliation of mica grains
• Weak slaty cleavage
• Represents low to medium grade metamorphism

Schistosity refers to the foliation of visible platy
minerals (e.g. mica) and/or linear alignment of
prismatic minerals (e.g. tourmaline or hornblende)
• Minerals are visible
• Rock is covered in scaly/glittering layer of shiny
minerals
• Can have wavy foliation
• Represents medium to high grade metamorphism

• Gneissic Banding refers to the alternating layers of
  light and dark minerals
  • Mineral size is medium to coarse (visible to eye)
  • Represents high-grade metamorphism

4 main texture types:
1. Crystalline (e.g. Marble)
2. Microcrystalline (e.g. Hornfels – Don’t worry about
this one)
3. Sandy (e.g. Quartzite)
4. Glassy (e.g. Anthracite)
*There are more than this but it will not apply to your
lab today*

Crystalline Texture: minerals are usually visible to the
eye and look like crystals. Crystals are usually all the
same size, and are medium to coarse grained.
• Can be all sorts of colors
• Some will fizz with HCL

• Sandy Texture: feels and looks like sand
• What could be the protolith?
• Very, very hard
• Composed almost purely out of fused quartz
grains (no porosity)

Represents low to medium grade metamorphism