5 Geology of Cordillera

Question 1

What was the original length of the rocky mountains before deformation and what is it right now?

Answer 1

The Rockies started off as a 300km stretch and is now 150km today

Question 2

What is the subduction zone called west of the insular belt and what is the plate that is being subducted?

Answer 2

The Cascadia Subduction zone and the Juan De Fuca Plate is being subducted

Question 3

How do geologists measure the displacement of the plates? (2)

Answer 3

1. mm/a (millimetres per year)
2. or km/Ma (kilometres per million years)

Question 4

What is the theory about the Juan de Fuca plate?

Answer 4

It started off as a much larger plate called the Farallon Plate and has become what it looks like today over the last ~56 million years ago (slide 15)

Question 5

What is the volcanic arc called that is the Cordillera?

Answer 5

Cascade volcanic arc

Question 6

What volcano in Canada erupted most recently?

Answer 6

Mount Meager

Question 7

What happened on the west coast 750Ma-550Ma?

Answer 7

Passive margin build-up of sediment

Question 8

What happened on the west coast 550Ma-~180Ma? (2)

Answer 8

1. Formation of island arcs off the coast that would eventually become the intermontane and insular belts
2. The formation of marine sedimentary rock build-up of the western margin of North America (the rocks you see in Banff)

Question 9

How many phases of deformation occurred in forming the Cordillera? How long ago was each phase?

Answer 9

Two Phases. 180Ma-100Ma for the first phase and 100Ma-55Ma

Question 10

What happened in the first phase deformation? (4)

Answer 10

1. First accretion event in intermontane belt ~180Ma
2. First period of deformation of intermontane belt 160Ma
3. First metamorphic episode in the Omenica belt
4. Folding and faulting to form the foreland fold and thrust belt

Question 11

What is the major geographic features of West Coast 100Ma?

Answer 11

There was a large basin to the east of the Cordillera (slide 43)

Question 12

What happened in the second phase of deformation? (4)

Answer 12

1. Second accretion event of terrane rocks in insular belt ~100Ma
2. Second deformation of intermontane and Omineca rocks
3. Second metamorphism of Omineca rocks
4. Formation of the Coast belt

Question 13

When was the collision of the insular belt with North America?

Answer 13

~100Ma

Question 14

When did the mountain building end?

Answer 14

55Ma

Question 15

What happened from 55Ma to 2Ma?

Answer 15

Erosion and exhumation of rocks at the surface expose metamorphic and igneous rocks that form deep in the mountain

Question 16

What has happened from 2Ma to the current?

Answer 16

Erosion and glaciation of the cordillera