Structure and chemistry of the Earth

Structure and chemistry of the Earth

Today’s topic:The chemistry of Earth’s mantle and crust

Iron meteorite

Chondrite meteorite

Meteorite compositiontells us about the chemistry of the earlyuniverse and Earth’score and mantle

Most meteoriteoriginate from asteroidbelt, but many are beingidentified 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 tooriginate at D” layer (otherwisecalled 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 magmasmust be able to form from partialmelting under mantle P-T conditions

Some mantle rocks have been recovered from deep ocean trenchesand by dredging

Pyrolite(3 peridotites:1 basalt)

Element Weight %

O 45.5

Si 26.8

Al 8.4

Fe 7.06

Ca 5.3

Mg 3.2

Na 2.3

K 0.90

Ti 0.5

Most abundant elements in the continental crust

The andesite model for continental crust:1 mafic:5 felsicresults in a chemical composition similar todiorite or andesite