An ultramafic plutonic rock composed of
olivine, orthopyroxene, and minor clinopyroxene. Harzburgite
is a common mantle rock found in the mantle sections of
ophiolites and deeply exhumed parts of the seafloor, such as
regions near large normal faults and near transform faults
and fracture zones. The harzburgite section of ophiolites and
oceanic mantle is typically strongly deformed into a harzburgite
tectonite, indicating very high shear strains formed during
flow of the mantle. This flow is thought to be upward
beneath the oceanic ridges and generally away from the
ridges closer to the surface and reflects mantle convection
and seafloor spreading. Oceanic harzburgites are also chemically
depleted, having had a basaltic melt extracted from
them during their rise beneath the oceanic ridges, and this
melt rose to form the oceanic crust above. The rocks are
named after occurrences in the Harz Mountains near
Harzburg, Germany.
See also OPHIOLITES.
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