Earth Structure and Composition Summary - Myweb @ CW Post

Mechanical Layers
lithosphere: strong, rigid crust plus uppermost mantle
asthenosphere: ~100-250 km, mantle near melting temp for that depth (pressure)
" weak, easily sheared, possibly/probably slightly molten (perhaps ~1%)
transition zone: ~410 km & ~660 km olivine changes to denser crystal structure
" olivine above 410 km
" spinel below 410 km
" perovskite below 660 km
lower mantle (also called mesosphere): 660 km - 2900 km, strong ultramafic rock
outer core: liquid iron/nickel
inner core: solid (or crystal mush) iron/nickel
Tectonic Settings (textbook section 1.4 & 1.5)
just a quickie review; detailed discussions of rock formation will come later
Divergent: Midocean Ridges:
two lithospheric plates separate
new crust forms by continuous formation and intrusion of mafic magma into fractures
ocean crust eventually receives a thin layer of ocean sediment (muds)
Convergent: Subduction Zones:
oceanic lithosphere sinks back down into the mantle at deep ocean trenches
mafic magma rises to form volcanic arc parallel to trench
sediments scraped off descending plate form accretionary wedge
Convergent: Continental Collisions:
continental crust is not dense enough to subduct - mountain building occurs
metamorphism of rock buried deep under mountain belt
mountains gradually weathered to produce sediments
Hotspot Tracks:
age-progressive chains of volcanoes (best seen on ocean crust)
more-or-less stationary plume of rising, hot mantle
melting as plume material nears base of lithosphere, produces mafic magma