8/3/2019 Plate Tec Key
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Key to Investigation 2: Plate Tectonics
1a. All three phenomena mostly appear concentrated on
continental edges, but this effect is secondary.
They are actually on pate boundaries. The edges of the
continental margins are either active plate
boundaries, such as the West Coast of the US, or they are
passive margins such as the East Coast of the
US. When Pangaea was forming about 300 million years ago, the
East Coast was an active margin,
with earthquakes, mountain building and volcanoes. The remnants
of these are still evident throughoutthe region.
1b. It is the moving of plates rubbing against each other that
cause earthquakes. Subduction zones are
primarily the cause of volcanoes. Converging or colliding plates
push up mountains. If plates are not
locally interacting with each other, there is little geologic
activity, such as in Central Australia, theGreat Plains (US) and
northern Europe.
1c. In most cases, plotted points will be on or very near plate
boundaries.
1d. The Earths crust is divided into about 20 plates that can
move in relation to one another. Because
Earths interior is so hot, partially melted rock carries that
heat toward the lower temperatures at thesurface (via convection
currents). These massive convection currents in the upper mantel
move theplates across Earths surface. Much of the heat is released
in spreading centers at midocean ridges,
which is the longest mountain range on Earth (46,000 miles
long). These spreading centers drive plate
movement, which is why there are many volcanoes and earthquakes
there.Each year, the Atlantic Ocean is widening by about two inches
(b/c of the reasons above).
North and South America are being pushed westward, and Europe
and Africa are moving eastward into
the Pacific Ocean, where colliding takes place, pushing up
mountain ranges and, in subduction zones,
producing volcanic chains of mountains.
2. Ring of Fire describes the coastline of the Pacific Ocean
because the whole region is one where
plates are converging and there are many volcanoes (due to
subduction zones).
3a-c. These two volcanoes are in the east Africa rift valley,
where there is a spreading center that is
moving in 3 directions, a triple junction. This same process
broke apart Pangaea 200 million years ago.Two of the directions are
flooded and under water, the Red Sea and the Gulf of Aden, where
Arabia
has been pulled from the African continent. In the third
direction, there has been much spreading, and
the crust has not stretched enough to fall below sea level and
flood. The volcanoes are a result ofmagma reaching the surface
through the thinned and stretched crust. The Red Sea may
someday
become another ocean.
In the eastern US, the same thing happened 200 million years ago
as Africa started to be pushed
away from the east Coast. The long linear basins of the East
Coast and Palisades (Jersey!), a volcanicsill, across the Hudson
River from New York City, are remnants of that spreading.
4a-d. Hot spots are thought to be plumes of magma that come from
deep in the mantle. The chemicalcomposition of magma is different
from subduction magmas in that they have little silica. The hot
spot
seems to remain in a fixed position in the mantle as the magma
burns through to the surface, producing
volcanic activity. As the tectonic plates move over these hot
spots, the magma burns through, leavinga trail of volcanoes.
The Hawaiian Islands are an example of such a trail of
volcanoes. In the continental US, the
hot spot that is now under Yellowstone National Park (the poor
quality picture) has burned its way
across the Snake River Plain and will probably continue into
southern Montana.
