This is a supplementary course presentation for basic petrology review in preparation to Applied Engineering Geology. The materials used in this presentation is mostly from Physical Geology - 2nd Edition by Steven Earle

1. A review
on rocks
and
minerals

2. What is a rock?
- consolidated mixture of minerals.
Consolidated means hard and
strong; real rocks don’t fall apart in
your hands.
mixture of minerals implies the
presence of more than one mineral
grain, but not necessarily more than
one type of mineral

3. Recall…
Igneous : formed from the cooling and
crystallization of magma (molten rock)
Sedimentary : formed when weathered fragments of
other rocks are buried, compressed, and
cemented together, or when minerals
precipitate directly from solution
Metamorphic : formed by alteration (due to heat,
pressure, and/or chemical action) of a pre-existing
igneous or sedimentary rock

4. Remember me??

5. Igneous Rocks
- Any crystalline rocks which is a product of cooling of a lava or magma

6. Magma and Magma Formation
igneous rocks that we see on Earth are derived from magmas that formed
from partial melting of existing rock

7. Analogy…

8. Mechanics of melting
Misconceptions: most partial melting of real rock does not
involve heating the rock up.
[Reduced pressure]

9. Common sites of magma formation in the upper mantle

10. Crystallization of Magma

11. Crystallization of Magma: A reflection topic

12. The chemical compositions of typical mafic, intermediate, and felsic
magmas and the types of rocks that form from them.

13. Examples of the igneous rocks that form from mafic, intermediate, and
felsic magmas.

14. Crystal fractionation

15. Porphyritic textures..

16. Classification of Igneous Rock
A guide to estimating the proportions of dark minerals in light-colored
rocks.

17. Intrusive
Igneous
Bodies

19. VOLCANISM

20. Plate Tectonics and Volcanism

21. Magma
Composition
and Eruption
Style

22. Variations in the volatile compositions of
magmas as a function of silica content
Explosive: eruption that
involves violent outcome
due to high volatile
content in a viscous
magma
Effusive: eruption that
involves a steady non-
violent flow of magma

23. Types of Volcanoes
Type Tectonic Setting Size and Shape
Magma and Eruption
Characteristics
Example
Cinder cone Various; some form on the
flanks of larger volcanoes
Small (10s to 100s of metres) and steep
(Greater than 20°)
Most are mafic and form from the gas-rich
early stages of a shield- or rift-associated
eruption
Eve Cone, northern
B.C.
Composite volcano
Almost all are at
subduction zones
Medium size (1000s of metres high and
up to 20 km across) and moderate
steepness (10° to 30°)
Magma composition varies from felsic to
mafic, and from explosive to effusive
Mount Mayon,
Kanlaon, St. Helens
Shield volcano
Most are at mantle
plumes; some are on
spreading ridges
Large (up to several 1,000 metres high
and up to 200 kilometres across), not
steep (typically 2° to 10°)
Magma is almost always mafic, and
eruptions are typically effusive, although
cinder cones are common on the flanks of
shield volcanoes
Kilauea, Hawaii
Large igneous
provinces
Associated with “super”
mantle plumes
Enormous (up to millions of square
kiometres) and 100s of metres thick
Magma is always mafic and individual flows
can be 10s of metres thick
Columbia River
basalts
Sea-floor volcanism
Generally associated with
spreading ridges but also
with mantle plumes
Large areas of the sea floor associated
with spreading ridges
Pillows form at typical eruption rates; lava
flows develop if the rare of flow is faster
Juan de Fuca ridge
Kimberlite Upper-mantle sourced
The remnants are typically 10s to 100s of
metres across
Most appear to have had explosive
eruptions forming cinder cones; the
youngest one is dated at about 10 ka, and
all others are at least 30 Ma
Lac de Gras
Kimberlite Field

24. Profiles of Mauna Loa shield volcano, Mount St. Helens composite volcano, and a
large cinder cone.
Comparison of profiles of volcanic landforms

25. Cinder Cones
• Typically, only a few hundred meters
in diameter, and few are more than
200 m high.
• Most are made up of fragments of
vesicular mafic rock (scoria) that
were expelled as the magma boiled
when it approached the surface,
creating fire fountains.

26. Composite Volcanoes
• associated with
subduction at
convergent plate
boundaries—either
ocean-continent or
ocean-ocean boundaries
• extend up to several
thousand meters from
the surrounding terrain,
with slopes ranging up to
30˚ They can be up to
about 20 km across.

27. As the rock cools it shrinks, and because it is very homogenous it shrinks in a
systematic way. When the rock breaks it does so with approximately 120˚ angles
between the fracture planes. The resulting columns tend to be 6-sided but 5- and
7-sided columns also form.

28. Most shield volcanoes are associated with mantle plumes, although
some form at divergent boundaries, either on land or on the sea floor

30. Sedimentary rocks
Rocks that are formed due to the lithification of
disintegrated materials from a parent rock or
precipitation of chemical compound.

31. Recall me, again..

32. Clastic sed rx Chemical sed rx
Precipitation
Lithification

33. Recall me, Karen..
The Udden-Wentworth grain-size scale for classifying sediments and the
grains that make up sedimentary rocks

34. Mechanics of particle settlement
(rule in sedimentation process)

35. Transportation
the ability of a moving medium (air or water) to move sedimentary
particles—and keep them moving—is dependent on the velocity of
flow.
At peak discharge, the water is high enough to flow over the
embankment on the right, and it flows fast enough to move the
boulders that cannot be moved during low flows.

36. Large bed load clasts are pushed (by traction) or bounced along the bottom
(by saltation), while smaller clasts are suspended in the water and kept
there by the turbulence of the flow

37. Lithification
Lithification involves the compaction of sediments and then the
cementation of grains by minerals that precipitate from groundwater in
the spaces between these grains.
Source: Karla Panchuk (2016) CC BY 4.0

38. Mudrock If it shows evidence of
bedding or fine laminations, it is shale;
otherwise, it is mudstone.

39. Sandstone
Arenite - clean
sandstone; one with
less than 15% silt
and clay
Arkosic arenites
have more than 10%
feldspar and more
feldspar than rock
fragments
Lithic arenites
have more than 10%
rock fragments, and
more rock fragments
than feldspar
A sandstone with more than 15% silt or clay is called a wacke
(pronounced wackie).

40. Sandstone in thin-section

41. Clastic
sedimentary
rocks
 Delicate sediments
preserve fossil
records
 Sand cross bedding
indicates changes
in directional
sequence of
current.
 Conglomerate
showing imbrication
indicating the flow
direction during
flood.
 Breccia indicates
complex
sedimentary
process

42. Chemical Sedimentary Rocks
sedimentary rocks that are dominated by components that have been
transported as ions in solution (Na+, Ca2+, HCO3−, etc.)
Most common: Limestone
Others include chert, banded iron formation, and
evaporites.
Biological processes are important in the formation of some chemical
sedimentary rocks, especially limestone and chert.

43. Limestone
-forms on the shallow continental shelves, especially in tropical
regions with coral reefs

44. (a) mollusc-rich limestone formed in a lagoon area, (b) foraminifera-rich sediment
from a submerged carbonate sandbar (c) ooids from a beach
Ooids – formed in offshore areas with strong currents where either
foraminifera tests accumulate, or calcite crystallizes inorganically

45. Limestone accumulates in deeper water, from the steady rain of the
carbonate shells of tiny organisms that lived near the ocean surface.
Carbonates formed in other environments:
Tufa: Springs Travertine: Hot springs
Speleothems: Caves

46. Carbonates formed in other environments:
Dolomite Chert
Banded Iron Formation
Evaporites: Salt & Potash (KCl)

47. Depositional Environments and Sedimentary Basins

48. The important terrestrial depositional environments and their
characteristics

49. The important marine depositional environments and their
characteristics

51. Original horizontality - sediments accumulate in essentially horizontal
layers. The implication is that tilted sedimentary layers observed today must
have been subjected to tectonic forces.
The principle of superposition - sedimentary layers are deposited in
sequence, and that unless the entire sequence has been turned over by
tectonic processes, the layers at the bottom are older than those at the top.
The principle of inclusions - any rock fragments in a sedimentary layer
must be older than the layer. For example, the cobbles in a conglomerate
must have been formed before the conglomerate was formed.
•
The principle of faunal succession - there is a well-defined order in
which organisms have evolved through geological time, and therefore the
identification of specific fossils in a rock can be used to determine its age.
Recall basic Principles of Geology

52. Bedding is
defined by
differences
in colour
and
texture,
and also
by
partings
(gaps)
between
beds that
may
otherwise
appear to be
similar.

53. Cross-bedding
is bedding that
contains
angled layers
within otherwise
horizontal beds,
and it forms
when sediments
are deposited by
flowing water or
wind
“the cross-beds dip down toward the right, implying a
consistent wind direction from right to left during
deposition”

54. How do cross-beds
form?

55. Graded bedding is characterized by a gradation in grain size from
bottom to top within a single bed.

56. Imbrication – general tilting of sediment particles parallel to the
direction of the flow.

57. In shallow body of water, muddy sediments have been deposited,
dries up and desiccated to for mud cracks

58. Groups, Formations, and Members
The main stratigraphic unit is a formation (ICS)
“The contrast in lithology between formations required to justify their
establishment varies with the complexity of the geology of a region and
the detail needed for geologic mapping and to work out its geologic
history. “
“No formation is considered justifiable and useful that cannot be
delineated at the scale of geologic mapping practiced in the region. The
thickness of formations may range from less than a meter to several
thousand meters”

59. A series of formations can be classified together to define a group
Groups, Formations, and Members
- could be as much as a few thousand metres thick, and
represents a series of rocks that were deposited within a
single basin
In areas where detailed geological information is needed, a formation might
be divided into members, where each member has a specific and
distinctive lithology.

60. Metamorphism and Metamorphic Rocks

61. Recall me, once more..

62. The main factors that control metamorphic processes
are:
• the mineral composition of the parent rock,
•the temperature at which metamorphism takes
place,
•the amount and type of pressure during
metamorphism,
•the types of fluids (mostly water) that are present
during metamorphism, and
•the amount of time available for metamorphism.

63. Parent Rock
1.the rock that exists before metamorphism
starts.
2.Sedimentary or igneous rocks can be
considered the parent rocks for
metamorphic rocks.
3.Albeit an existing metamorphic rock can be
further metamorphosed, or re-
metamorphosed, metamorphic rock
doesn’t normally qualify as a “parent
rock”.

64. Temperature
 mineral stability is a function of temperature, pressure, and
the presence of fluids (especially water).
 All minerals are stable over a specific range of temperatures.
For example, quartz is stable from environmental temperatures
(whatever the weather can throw at it) all the way up to about 1800°C.
 If the pressure is higher, that upper limit will be even higher.
 If there is water present, it will be lower.
 On the other hand, most clay minerals are only stable up to about
150° or 200°C; above that, they transform into micas.

65. Some minerals
will crystallize
into different
polymorphs
 The minerals
kyanite,
andalusite, and
sillimanite are
polymorphs with
the composition
Al2SiO5

66. Pressure
Rocks that are subjected to very high confining pressures are
typically denser than others because the mineral grains are
squeezed together

67. Fluids
 Water is the main fluid present within rocks of the crust.
 Water facilitates the transfer of ions between minerals and
within minerals, and therefore increases the rates at which
metamorphic reactions take place
 hot water, can have elevated concentrations of dissolved
elements (ions), and therefore it is an important medium for
moving certain elements around within the crust
Time
 most metamorphic reactions take place at very slow rates;
 the growth of new minerals within a rock during metamorphism has been
estimated to be about 1 millimeter per million years

68. Classification of
Metamorphic
Rocks

69. The textural effects of squeezing and mineral growth during regional
metamorphism.
The left diagram is shale with bedding slanting down to the right. The right
diagram represents schist (derived from that shale), with mica crystals orientated
perpendicular to the main stress direction and the original bedding no longer easily
visible

71. The various types of foliated metamorphic rocks, listed in order of the
grade or intensity of metamorphism.

72. Slate is formed from the low-grade metamorphism of shale and tends to
break into flat sheets.
Phyllite is like slate but has typically been heated to a higher temperature
Schist is a medium-grade metamorphic rock formed from mudstone or
shale;
Gneiss has little or no mica because it forms at temperatures higher than
those phyllite which micas are stable.
Variety: Amphibolite if gneiss originated as basalt dominated by
amphibole (amphibole gneiss)

73. Migmatite

74. A rough guide to the types of metamorphic rocks that form from different
parent rocks at different grades of regional metamorphism.

75. Non-foliated Metamorphic Rocks
form under either low-pressure conditions or just confining pressure
Ex: Contact Metamorphism
- the heat for the metamorphism comes from a body of magma that has
moved into the upper part of the crust

76. Regional Metamorphism
Note: Quartzite (like marble) does not tend to look foliated because quartz
crystals don’t align with the directional pressure during regional
metamorphism.
- associated with the major events of Earth dynamics, and most metamorphic
rocks are so produced.
Quartzite Quartzite under ppl

77. Hornfels is another non-
foliated metamorphic rock that
normally forms during contact
metamorphism of fine-grained
rocks like mudstone or
volcanic rock.

78. Plate Tectonics and Metamorphism
Most regional metamorphism takes place within the continental crust (e.g.,
Himalayan Range)
Relationships between plate tectonics and metamorphism

79. Regional metamorphism
beneath a mountain
range related to
continent-continent
collision (typical
geothermal gradient).
Metamorphic rocks
formed here are likely
to be foliated because
of the strong directional
pressure (compression)
of converging plates

80.  Water within the crust is forced to rise in the area close to the source of
volcanic heat
 Such passage of water through the oceanic crust at 200° to 300°C promotes
metamorphic reactions
Retrograde
metamorphism is a
metamorphism that
takes place at
temperatures well
below the temperature
at which the rock
originally formed
(~1200°C)
Example:
greenstone (not foliated)
or greenschist (foliated)

81. Regional Metamorphism
Metamorphic index minerals and their approximate temperature ranges
 occurs when rocks are buried deep in the crust
 commonly associated with convergent plate boundaries and the
formation of mountain ranges
 the areas affected tend to be large—thousands of square kilometers.

82. A special type of
metamorphism takes
place under very high-
pressure but relatively
low-temperature
conditions
Regional metamorphism of oceanic crust at a subduction zone
 produces an amphibole
mineral known as
glaucophane
(Na2(Mg3Al2)Si8O22(
OH)2) and is an
important component of
blueschist.
Note: Higher grades of metamorphism can take place closer to surface than is the
case in other areas.

83. Contact Metamorphism and Hydrothermal
Processes
 takes place where a body of
magma intrudes into the
upper part of the crust.
 any type of magma body can
lead to contact metamorphism,
from a thin dyke to a large
stock.
 contact metamorphic aureoles
are typically quite small (dykes
and sills) to several 10s of
meters around a large stock

84. Contact
metamorphism
- happens at relatively
shallow depths, in the
absence of directed
pressure
Results: Rock does
not normally develop
foliation
d. Contact metamorphism around a high-level crustal magma chamber;
e. Regional metamorphism in a volcanic-arc related mountain range
(volcanic-region temperature gradient)

85. Zone of contact metamorphism
- the main process is to transfer the heat from the pluton to the
surrounding rock
In this situation mud rock or volcanic rock will likely be metamorphosed to
hornfels

86. Metasomatism
- much of the change is derived from fluids passing through the rock.
Ex: Skarn
A special type of metasomatism that took place where a hot pluton intrudes
into carbonate rock such as limestone
Skarn
Calcite veins in limestone

87. Types of metamorphism shown in the context of depth and temperature under
different conditions

88. Thank you!
Gising ka
na!