Mantle plumes and continental rifting
Reading pages
488-490
Figure
19.41 mantle plume rising under
continental crust
Figure 19.43 continental break-up caused by an erupting mantle plume
Figure 19.44 Afar triple junction, Red Sea, and Gulf of Aden
Figure 19.45 two mantle plumes and continental rifting
According to Wegener, the continents are sections of a super-continent called Pangea that was together about 200 million years ago
Evidence: A reconstructed position of the continents “makes sense” in explaining the distribution of
· Continental fit Figure 19.11
Distribution of fossils
· Figure 19.3
Glacial deposits
· Figure 19.4
Mountain Belts
Permian position of the North Pole relative to North America seems to be in China
Earth’s
Magnetic Field
reading in
Chapter 17, pgs. 428-433
Figure 17.21 Lines of electromagnetic force arc out into space from the South Pole and return at the North Pole
The spin of the solid inner core inside the liquid
outer core produces the magnetic field
Chap 17 Box 4
Magnetic field is recorded as lava cools
Figure 17.22 alignment of magnetite in lava with the
Earth’s magnetic field
Curie point and magnetic domains
(p. 429)
Figure 19.10 The paths of the wandering North Pole are different for North America and Europe, and are far away from the modern pole
Example: Permian climate zones
Figure 19.5
The climate zones represented by Permian sedimentary rocks generally don’t make sense if the apparent North Pole is used as the Earth’s axis; but the climate zones are reasonable if the ancient pole position is placed near the present North Pole
Important point
– there are two options here:
(1)
the continents stayed in the same place but the poles moved; or
(2)
the poles stayed in approximately the same place, but the continents moved
Pre-Pangea:
Laurasia (northern mega-continent; Laurentia and Asia)
North America
Europe
Asia
Gondwana (southern mega-continent)
Africa
South America
Antarctica
India
Australia
Panthalassa (world ocean)
Figure 19.2 break-up of Pangea from Permian to present
Figure 19.7
According to Wegener’s theory, the fragments of Pangea plowed through the oceanic crust, to their present locations.
There
was no known mechanism that would allow this, and most scientists dismissed
Wegener’s ideas.
Figure 19.6
Magnetometers were originally developed to search for submarines
Surveyors noticed regular changes in the background signal
Advances
in science during the 1940s and 1950s were largely the result of technology
developed for military applications
Figure 19.14 magnetic lineations at the mid-ocean ridge
positive anomalies – normal magnetic polarity (magnetic north is at the geographic North Pole)
negative anomalies – reversed magnetic polarity
Two key pieces of information:
Age
Magnetic Direction
May be recorded in igneous rocks, such as layers of a volcano
(It’s easier to take measurements and collect samples on land.)
Magnetic Inclination Figure 17.21
Parallel to surface at the equator
Straight down at the North Pole
Straight up at the South Pole
Telling magnetic direction
from a rock Figure 19.8
Developed from many
measurements of igneous rocks:
Magnetic direction &
Age
of rock
Figure 19.15
Use the paleomagnetic timescale to determine the age of the
magnetic anomalies at the mid-ocean
ridge
The process of forming a magnetic lineation by mid-ocean ridge spreading Figures
19.16, 19.17
Age of the North Atlantic Ocean basin
Figure 19.18
Age of the world ocean basins