Class Notes- Unit 6

Question 1

What is the early evidence of Pangea?

Answer 1

1) Jig-saw puzzle fit of continents
2) Matching rocks across oceans (pre-breakup rocks)
3) Matching fossils across (pre-breakup living environments)

Question 2

What are causes and/or controls either totally or partially of plate tectonics?

Answer 2

• earthquakes
• volcanism
• topography/scenery/mtn. belts
• climate
• organic evolution
• jig-saw puzzle fit of continents

Question 3

What explains the causes and/or controls of plate tectonics?

Answer 3

-rock matching across D.P.B (some oceans)
-Paleomagnetic features
(apparent polar wandering, sea floor magnetic stripes)

Question 4

What is the mid-late 20th C. evidence of Pangea?

Answer 4

Structure of the lithosphere
Includes: mid oceanic ridges; oceanic trenches; structure of continents; earthquakes; volcanoes; paleomagnetism; tectonic mountains

Question 5

What is modern evidence of Pangea?

Answer 5

• Increasing detail of evidence from 20th C.

- Satelliet mapping

Question 6

What is the rate of movement for a continent per year?

Answer 6

2 cm/year

Question 7

Continent movement rate can vary from___.

Answer 7

0-10 cm/year

Question 8

What did Wegner divide northern and southern continents into?

Answer 8

Laurasia and Gondwana

Question 9

Matching rocks across Gondwana–___between___America and___.

Answer 9

• Archean
• South
• Africa

Question 10

What were the two fossils studied that matched fossils across the continents?

Answer 10

• Mesosaurus (shallow-marine reptile coastal)

- Glossopteris (leafs)

Question 11

What is the range of the mesosaurus?

Answer 11

Range 299-280 Ma

Question 12

What is the range of the glossopteris?

Answer 12

299-251 Ma

Question 13

What is significant out the Appalachians?

Answer 13

Rocks of this mountain belt run straight out to sea and then truncate (rock matching because these same rocks are found on the coast of the N.A, Greenland, Europe).

Question 14

What are the 6 steps of apparent polar wandering to calculate the movement of continents?

Answer 14

1. Measure magnetic vector in rock (lava especially)
2. Calculate VGP (virtual geomagnetic pole)
3. Determine the absolute age of the rock
4. Do this for a number of different rock ages and plot all the VGPs on a map–for one continent
5. In every case we see a line–succession–of VGPs. This line of “apparent polar wandering”
6. Compare these lines for the various continents. We have now done this for every continent back to about 3.0 Ga for some.

Question 15

Where do most of the worlds most active geology (volcanoes and earthquakes) take place?

Answer 15

occurs at divergent and converged plate countries.

Question 16

What is relative plate movement?

Answer 16

Defines the plate boundaries

Question 17

What is absolute plate movement based on today and in the past?

Answer 17

1. today satellite GPS surveying

2. in the past…paleomagnetic apparent polar wandering

Question 18

What are precambrian regions built up from?

Answer 18

Ancient orogens

Question 19

What is the part of a continent that is geologically stable?

Answer 19

Ancient craton

Question 20

Where do earthquakes occur?

Answer 20

Earthquakes occur at Plate Margins where rock breaks, either by being pulled apart or compressed “Earthquake Zones”

Question 21

What is the Earthquake focus?

Answer 21

Spot within the earth where the maximum energy is released

Question 22

What is the earthquake epicentre?

Answer 22

Spot on EArth’s surface directly above the focus

Question 23

Where will the earthquake epicentre be with a vertical fault?

Answer 23

On the fault line

Question 24

Where will the epicentre of an earthquake be when the fault line is not vertical?

Answer 24

not on the fault line

Question 25

Where do Earthquakes and visible volcanoes mostly occur?

Answer 25

• occur mainly at places where plates collide (Convergent Plate Boundaries)
• but also where they separate (Divergent Plate Boundaries)

Question 26

___but not___occur where plates slip sideways past each other (Transform Plate Boundary).

Answer 26

Earthquakes but not volcanoes

Question 27

___but not major___occur inside some plates at “hot spots.”

Answer 27

Volcanoes but not major earthquakes

Question 28

What do divergent plate boundaries result in the formation of?

Answer 28

• earthquake zones
• mid-ocean ridges and rises
• volcanism
• creation of new crust
• opens ocean basins

Question 29

“Divergence” produces…?

Answer 29

Extension which can result in NORMAL Faults (also called “extensional faults”).

Question 30

Where are normal faults produced?

Answer 30

Anywhere the EArth’s crust is being horizontally stretched.

Question 31

What’s happening near the top of plume?

Answer 31

decompression melting at MOR

Question 32

What is plume?

Answer 32

• A mantle plume is an upwelling of abnormally hot rock within the Earth’s mantle
• As the heads of mantle plumes can partly melt when they reach shallow depths, they are often invoked as the cause of volcanic hotspots, such as Hawaii or Iceland, and flood basalts such as the Deccan and Siberian traps. Some such volcanic regions lie far from tectonic plate boundaries, while others represent unusually large-volume volcanism near plate boundaries or in large igneous provinces.

Question 33

What is partial melting?

Answer 33

Some rock components melt at lower temperature than others.

Question 34

What kind of melting does decompression melting at MOR produce?

Answer 34

partial melting

Question 35

With decompression melting at MOR, what happens as magma rises in the plume?

Answer 35

• At first it is hot (2000 degrees C) and a high pressure keeps it solid.
• As it rises it is still hot (1100 degrees C) but at a lower pressure so decompression melting – partial melting – takes place.

Question 36

What is the distance between sea level and the asthenosphere?

Answer 36

100 km

Question 37

On average, how long is a diverging MOR?

Answer 37

88 000 km long

Question 38

What is the 4 step evolutionary sequence for continental breakup?

Answer 38

1) Mantle plume under pre-existing continent that begins to separate the continent
2) A rift valley forms as the two sections separate by graben filled with lava
3) Linear sea forms
4) Ocean forms

Question 39

What is a graben?

Answer 39

a graben is a depressed block of the Earth’s crust bordered by parallel faults.

Question 40

What 3 things were determined by the evolutionary sequence of continental breakup?

• how do rocks of sea floor form?
• where is the youngest sea floor rock located?
• where are lower and higher intensity bands and what do these bands represent?

Answer 40

1) rocks of sea floor form from lava decompression melting at plume–recycling rock from the mantle to the crust
2) Lava closer to ridge is younger, and lava farther from ridge is older
3) Sea floor rocks varied in intensity of magnetism in long strips. Lower intensity bands are places were magma has reverse polarity and high intensity where lava has normal magnetic polarity.

Question 41

What happens as new basalt is added to the ocean floor at the MOR (divergence, the sea floor, and paleomagnetism)?

Answer 41

It becomes magnetized according to the earth’s field at that time. Divergence carries this basalt away to both sides of the MOR an new basalt takes it place.

Question 42

What type of sea floor rock does the occasional field reversal produce?

Answer 42

The occasional field reversal produces bands of normal and reversed magnetic polarized sea floor rock. Much like a tape recorder.

Question 43

What do the sea floor rocks record?

Answer 43

Long history of paleomagnetic reversal

Question 44

What confirms plate divergence is taking place?

Answer 44

• Rock ages on sea floor (basalt lava record)

- Earth’s magnetic polarity