Glossary - The Solid Earth - page 660

lithosphere the rigid outer skin of the Earth, which includes the crust and the uppermost
mantle; its base is defined either mechanically by strength, or thermally as the level above
which heat is dominantly transferred by conduction.
LLLAMA large laterally linked Archaean magma anomaly; see Section 10.5 .
longitude angular distance east or west of the prime meridian (which passes through
Greenwich, U.K.) of a point on the Earth's surface.
Love wave surface wave for which the particle motion is transverse and orthogonal to the
direction of propagation of the wave.
low-pass filter filters the signal to remove frequencies above a given frequency, passes only
the low frequencies.
Ma million years, mega-annum.
mafic rock rock rich in magnesium ( ma ) and iron ( fic ) minerals.
magma molten rock when it is within the Earth.
magmatism development and movement of magma.
magnetic anomaly difference between observed (measured) and theoretical values of the
magnetic field.
magnetic poles ends of a permanent bar magnet; by convention, lines of force leave the north
pole of the magnet and enter its south pole.
magnetic variation see declination.
magnetometer instrument that measures the Earth's magnetic field.
major elements the major components of the earth's crust: O, Si, Al, Fe, Ca, Na, K and Mg;
in geochemical work, also Ti and P.
mantle solid shell of the Earth extending from the crust to the core; divided into the upper
mantle (from the Moho down to 670 km depth) and the lower mantle (from 670 to 2891 km
depth, 2891 km being the depth of the core-mantle boundary).
metamorphic grade recorded temperature of metamorphism; sometimes, but less correctly,
used to imply pressure.
metamorphic rocks rocks that have been changed from their original state, usually by
temperature or pressure.
metamorphism changes in mineralogy and texture of a rock caused by temperature and
pressure.
minerals crystals that make up rocks.
Moho seismic boundary between the crust and the mantle; named after A. Mohorovicic.
molasse sedimentary rocks that are deposited in a fore-arc basin in front of a thrust-up
mountain belt; often includes thick sandstones, conglomerates and shales.