EPSC201 - Lecture 10 Notes
Last nights earthquake was around 4.5 on the
Richter scale, and was rather deep focus. This
earthquake was on a fault line. This fault had a little bit of move-
ment on it, which caused the earthquake. The probable cause is
elastic rebound from the last glaciation. At one point there was
a few km of ice on top of the crust in the Montreal area, and
now the crust is trying to bounce back upwards. In a geologi-
cal time scales, the last ice age was extremely recent, and the
crust is still rebounding.
The aftershocks from this earthquake will be extremely small. They
will be in the next day or two after the initial earthquake.
Key point – glacier pushes plate downwards because its heavy, when it
melts the plate bounces back upwards
Perturba- tions in the mantle- core boundary cause mantle to be melted by the hot
core, and rise up a mantle plume. This plume is a verticle column of hot rising material.
As it rises, it is under less pressure, and the hot material melts into a liquid. This is called
decompression melting. The plume seems to be stationary for millions of
years. The evidence of this is the linear chain of islands formed over hot spots.
The plates are moving over a stationary plume, which causes a chain of islands to form. Presumably, over
a long period of time, the plume will collapse and quit producing islands. The temperature in plumes in
constant for a long time, but will eventually cool down. The islands can be dated, by surface rock analysis,
and the distance between them can be measured. Thus, you can measure the velocity of the plate, and
see if the plate has changed speed over time.
Not all of the volcanoes formed by the hot spot make it to
the surface. The underwater area is very bumpy.
The chain of islands produced by a hot spot can show the di-
rection the plates have moved over time. There are rocks in
India from a hot spot in the Indian sea. This shows the Indi-
an sub-continent moved from Antarctica northwards.
Continental rifting is occurring between Africa and Arabia.
The two plates are moving apart, and an ocean is flowing in
between. The spreading occurs from mantle uprising, which
could be caused by mantle convection, or a hot spot. This
causes the crust to be stretched out and thinned. As the crust
is thin, it melts easier, and turns into lava and volcanoes. Even-
tually the two plates will separate. Continental rifting is essentially
the same as sea floor spreading. The crust is old because it doesn’t subduct. The ocean floor is very young.
Remember, the asthenosphere is ductile. The mantle is solid. The outer core is liquid, the inner core is
Mineralogy – Minerals and Crystals:
A crystal is a manifestation of a mineral. A mineral is a solid that has a specific chemical composition.
Quartz has a chemical composition of SiO2. Halite is NaCl, also known as salt. Minerals are manifested
Wikipedia – minerals are a naturally occurring solid, represented by a chemical formula, and have ordered
atomic structure. They differ from rocks, which are made of many different chemicals The crystal represents the geometric form that that mineral takes. Halite
forms a cube. Quartz forms a hexagon shape with a pyramid on top.
Crystals can be very big. In mines, they are found at sizes of up to
30 meters long. While the length and diameter can vary, the shape
is exactly the same.
Gypsum – the mineral CaSO4·2H2O. There was a big mine in
Mexico that found a cave of huge gypsum crystals.
To grow crystals, you evaporate the water very s