Structure and chemistry of the Earth
Today’s topic:
The chemistry of Earth’s mantle and crust
Iron meteorite
Meteorite composition
tells us about the
chemistry of the early
universe and Earth’s
core and mantle
Chondrite meteorite
Most meteorite
originate from asteroid
belt, but many are being
identified from the
Moon and Mars
Moho
Core-mantle boundary
(Gutenberg discontinuity)
Inner core-outer core boundary
(Lehmann discontinuity)
Moho
-discovery published c. 1910-12 by
a Yugoslavian after a 1906? quake
in Europe
Core-mantle boundary
- discovered by Oldham after
M8 in 1896 in Assam, India
Inner core-outer core boundary
- discovered in the 1930s by a Dane
• Crust synonymous with lithosphere
until the 1950s
• 440 km discontinuity = change in
olivine structure (spinel or
ringwoodite phase)
• 660 km discontinuity = transform
all minerals into perovskite and
minor Fe-Mg oxide (Mg-wustite)
Upper mantle-lower mantle
boundary
Mantle plumes thought to
originate at D” layer (otherwise
called a ‘mantle upwelling’)
New science!
The inner core rotates faster
than the earth
Mantle composition
Estimated from ultramafic
xenoliths and stony meteorites,
geophysical requirements for
density and seismic velocities,
heat production from decay of
U, Th, and K, and basaltic magmas
must be able to form from partial
melting under mantle P-T conditions
Some mantle rocks have been
recovered from deep ocean trenches
and by dredging
Pyrolite
(3 peridotites:1 basalt)
Most abundant elements in the continental crust
Element
O
Si
Al
Fe
Ca
Mg
Na
K
Ti
Weight %
45.5
26.8
8.4
7.06
5.3
3.2
2.3
0.90
0.5
The andesite model for
continental crust:
1 mafic:5 felsic
results in a chemical
composition similar to
diorite or andesite