Transition zone (Earth)

The transition zone is the part of <a href="/facts/Earth/HLLmDfj0">Earth</a>'s <a href="/facts/Mantle_(geology)/RpDdtjCr">mantle</a> that is located between the <a href="/facts/Lower_mantle_(Earth)/KQQBHWp8">lower</a> and the <a href="/facts/Upper_mantle_(Earth)/5I9jq18K">upper mantle</a>, most strictly between the seismic-discontinuity depths of about 410 to 660 kilometres (250 to 410 mi), but more broadly defined as the zone encompassing those discontinuities, i.e., between about 300 and 850 kilometres (190 and 530 mi) depth. Earth's solid, rocky <a href="/facts/Earth%27s_mantle/l9DjRLcc"> mantle</a>, including the mantle transition zone (often abbreviated as MTZ), consists primarily of <a href="/facts/Peridotite/4NRPpWxw">peridotite</a>, an <a href="/facts/Ultramafic_rock/7qAapP1d">ultramafic</a> <a href="/facts/Igneous_rock/xeMJhUah">igneous rock</a>.
The mantle was divided into the upper mantle, transition zone, and lower mantle as a result of sudden <a href="/facts/Seismic/Lony1LYX">seismic</a>-velocity discontinuities at depths of 410 and 660 kilometres (250 and 410 mi). This is thought[by whom?] to occur as a result of rearrangement of grains in <a href="/facts/Olivine/tLLL4rae">olivine</a> (which constitutes a large portion of peridotite) at a depth of 410 kilometres (250 mi), to form a denser crystal structure as a result of the increase in pressure with increasing depth. Below a depth of 660 kilometres (410 mi), evidence suggests due to pressure changes ringwoodite minerals change into two new denser phases, bridgmanite and periclase. This can be seen using <a href="/facts/Body_wave_(seismology)/1JTeLfac">body waves</a> from <a href="/facts/Earthquake/NGjIzagw">earthquakes</a>, which are converted, reflected or refracted at the boundary, and predicted from <a href="/facts/Mineral_physics/gxxfLNev">mineral physics</a>, as the phase changes are temperature and density-dependent and hence depth dependent.

Transition zone (Earth) open-in-new

Transition zone (Earth)