Geology 1023

Cordillera and Appalachians

Orogenic (mobile) belts

• At the edges of continents

• Platform sequence that gets buckled by collision

• Also volcanism, plutonism, metamorphism and accretion of terranes

• Exercise in 3 parts

Doing the lab. Q. 1

• On p. 2, 3, and 4, maps of part of the Cordillera (front ranges in Alberta)

• Rocks are folded and thrust into stacked layers and folds

• For each map draw a cross-section

• In each section see some of the stratigraphy

• Information from all three maps allows you to put the whole sequence in order

Fill in with colour or pattern

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Don’t colour too far down. We don’t know what’s here

Doing the lab. Q. 1

• Once you’ve completed Fig. 1 you will know the order of some of the units (look at patterns)

• Complete Fig. 2

• This will give you more of the sequence.

• Complete Fig. 3

• This will allow you to complete the sequence

Doing the lab. Q. 1

• Things to watch out for:

• Draw contacts as straight and parallel (use a ruler and protractor).

• USE THE SAME COLOUR FOR EACH UNIT ON EACH MAP

• Information from Fig. 1 will tell you about hidden units on Fig. 2 and Fig. 3.

Doing the lab. Q 1

• Using the information you’ve determined from completing the figures, fill in the blank column given on p. 6– USE THE SAME COLOURS AS YOU USED ON

THE MAPS

• The names of each of the units and their patterns are given on p. 5 (where they are not in stratigraphic order).

• The abbreviation used for each unit gives its age.

Abbreviations for rock ages• K = Cretaceous

• J = Jurassic

• T = Triassic

• P = Permian

• P = Pennsylvanian

• M = Mississippian

• D = Devonian

• S = Silurian

• O = Ordovician

• C = Cambrian

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R

Doing the lab. Q 1

• Look at the representative samples at the back of the lab and give a brief lithological description/name for the unit (e.g., green siltstone, fossiliferous limestone, grey shale, quartz-pebble conglomerate, etc.)

Canmore map sheet. Q. 2• Shows part of the Rocky Mountains near

Canmore

• Divided into two halves (East and West)

• Thrust faults shown as lines with triangular ticks

• Strike is the general trend of the fault trace

• Triangles indicate direction of dip

• Triangles point opposite to thrust direction

strike

dip

thrust direction

Calculating shortening.

Calculating shortening.

Calculating shortening.

Calculating shortening.

Calculating shortening.

Calculating shortening.

Shortening in the Canmore area.

• Measure the length of each segment of the Devonian Southesk Formation (DSX) in cross section 2. Total should be at least 40 km.

• Map scale is 1:50,000. Therefore length in kilometers = length in centimeters/2

• Measure the current length into which the Southesk formation has been compressed

• Calculate shortening (λ)

Appalachian orogen. Q. 3.• Appalachians are older and more deeply eroded than

the Cordillera

• Legend, (top left) is arranged to show different major tectonic slices or terranes (originally called zones by Williams)

• a) See which colour represents basement and find the best Canadian example.

• b) Thrusts are present throughout the orogen but the best example occurs in the southeastern U. S. in an area whose name describes the topography formed by folds and thrusts

Appalachian orogen. Q. 3.• c) Strike is the average direction of the thrust (give as

general compass direction e.g., NE). Dip is the direction that the triangles point (give as general compass direction, e.g., NW)

• d) Direction of thrust is the opposite of the dip.– Note: North is top right on this map

• e) Read the legend to see what colour is used to represent ophiolites. Find the best Canadian example.

• f) What are ophiolites. If you can’t remember look them up in your textbook.

Questions?