RECORDS OF GEOLOGIC PROCESSES

Sedimentary rocks comprise a majority of the surface of the Earth, but are a minor volume of the total volume of the crust... IGNEOUS ROCKS 地地地 Definition: A rock formed by the solidi

RECORDS

OF GEOLOGIC PROCESSES

( 地地地地地地地 )

ROCK , by definition,

is composed of an aggregate of

minerals ( 地地 )

( 地地 )

• Appearance of a rock is related to:

1 Mineralogy = types and relative proportions of constituent minerals

2 Texture = size, shape and orientation of mineral grains

• These features relate to the origin and history of the rock.

When many rocks are understood, the geologic history (and

Where do we see rocks?

• Not on the

surface of course!

• They are at

depth in most places covered by soil and regolith ( 地地地 ).

Three general rock types:

1 Igneous - formed by solidification of molten rock (>700 ° C)

2 Sedimentary - formed as burial products of sediments , on land or sea

3.Metamorphic - formed by transformation in the solid state of pre-existing rock due to

changing pressure and temperature.

( 地地地 )

( 地地地 )

( 地地地 )

Sedimentary rocks comprise a

majority of the surface of the Earth, but are a minor volume of the total volume of the crust

IGNEOUS ROCKS ( 地地地 ) Definition: A rock formed by the solidification of magma (molten rock)

Igneous environments

IGNEOUS ROCKS ( 地地地 )

• Can be intrusive (crystallizing below the surface of the Earth) or extrusive (crystallizing at the surface

of the Earth)

• Textures in igneous rocks relates

to the composition of the magma,

rate of cooling of the magma and

any flow features of the magma

• Extrusive ( 地地 ) rocks - rapid

cooling, therefore fine-grained or

glassy; some surface flows

• Intrusive ( 地地 ) rocks - slower

cooling, therefore coarser grained;

flow features possible



IGNEOUS ROCKS ( 地地地 )

SEDIMENTARY ROCKS ( 地地地 )

Definition: A rock formed by the accumulation and

cementation of mineral grains by wind, water or ice

transportation to the site of deposition, or by chemical

precipitation at the site.

Typical sedimentary

• Sedimentary rocks - generally characterized by bedding i.e

parallel layers of sediments

• Textures of sedimentary rocks relate to the manner of sediment

transport and deposition e.g high vs low velocity transport

• This is an interface between the atmosphere, hydrosphere and

SEDIMENTARY ROCKS ( 地地地 )

• Types:

1 Clastic - physically deposited sedimentary particles

(clasts - broken rocks, remains or products of animals or plants) transported and laid down by running water,

wind or ice Generally silicate minerals.

2 Chemical and biochemical sediments

-chemical precipitation of dissolved

components of rocks at the

depositional site e.g halite, calcite

3 Mixtures of both of the above

• Lithification of sedimentary rocks –

hardening into a solid rock due to

compaction and cementation



METAMORPHIC ROCKS ( 地地地 )

Definition: A rock whose original mineralogy, texture, or composition has been changed by the effects of pressure, temperature, or the gain or loss of chemical components.

• Occurs between temperatures of roughly 250°C (end of

sedimentary lithification processes) and melting of the rock

(>700°C) Contact and regional metamorphism

at plate-collisional mountain ranges

Contact and regional metamorphism at subduction zones

METAMORPHIC ROCKS( 地地地 )

• General classification of type of metamorphism relates to location of heat source

1 Regional metamorphism - heat

source in not apparent, but

generally higher; associated with

mountain building episodes

extending over large regions

2 Contact metamorphism - heat

source is apparent i.e associated

with intrusion of a magma that

"cooks" the surrounding rocks

• Textures relate to the pressure,

temperature and deformational

history of metamorphic rock



Metamorphic environments

THE ROCK CYCLE ( 地地地地 )

• Inter-relationships among the three rock types

• The rock cycle is directly related to plate tectonics ( 地地

地地 ) - in turn, the rocks that we currently see can infer tectonic conditions in the past.

• This is an

interaction

among the

atmosphere,

hydrosphere,

lithosphere and asthenosphere

(the mantle

layer) and is

unique to Earth

Recommended Web-sites:

Chinese web-site:

岩石圈

English web-sites:

Discover How Rocks Are Formed

Rocks For Kids

Your Gemologist

Rockdoctors

Guide to Minerals, Igneous, Metamorphic, and Sedimen