Slide 2 1; movies Slide 3 Topography of a fast spreading ridge
(EPR) Slide 4 Topography of a slow spreading ridge (south atlantic)
Slide 5 2; topography Slide 6 Slide 7 Melt beneath a fast-spreading
ridge (East Pacific Rise) Slide 8 Ophiolites Slide 9 3; classic
ophiolites Slide 10 Oman ophiolite Slide 11 Pillow lavas Slide 12
Sheeted Dikes Slide 13 Layered Gabbros Slide 14 V s is the
particles' settling velocity (vertically downwards if p > f,
upwards if p < f ) g is the acceleration due to gravity, p is
the density of the particles, and f is the density of the fluid
Stokes law Slide 15 4; settling Slide 16 Massive gabbro Slide 17
Impregnated dunnite Banded harzburgite Slide 18 Slide 19 Hot spot
volcanism: a global phenomenon Slide 20 5; Hawaii-emperor chain
Slide 21 The origin of hot spot volcanoes from melting of plumes
Slide 22 Dynamic models of mantle convection Plates going down
Plumes coming up Rapid, small-cell convection on Io Slide 23 Why
does the mantle melt to produce hot spot magmas? Isentropic
decompression melting Fluxing by volatiles Heating of the
lithosphere by a hot plume Unconventional heat sources Slide 24
Simple variations on the decompression melting theme Variations in
potential temperature -- hotter mantle produces deeper melting,
more magma Variations in the thickness of the lithosphere --
controls the depth at which melting terminates Fractional vs. batch
melting All of these can vary from hot spot to hot spot and within
a single volcano, producing distinctive chemical signatures Slide
25 Slide 26 Temperature variations near head of plume 3D Model by
Ribe and Christensen Slide 27 Why does the mantle melt to produce
hot spot magmas? Isentropic decompression melting Fluxing by
volatiles Heating of the lithosphere by a hot plume Unconventional
heat sources Slide 28 Why does the mantle melt to produce hot spot
magmas? Isentropic decompression melting Fluxing by volatiles
Heating of the lithosphere by a hot plume Unconventional heat
sources Slide 29 Hawaii (topography/bathymetry) Slide 30 Geological
map of the big island of Hawaii Slide 31 Slide 32 HSDP drilling in
1993 and 1999 into the flank of Mauna Kea volcano >95% recovery,
to a total depth of 3.1 km below sea level Penetration through ~1
km of subaerial lavas, ~2 km of submarine deposits, both
hyaloclastites and pillows Slide 33 estimate of average subsidence
rate Slide 34 Slide 35 hyaloclastite formation -- prograding delta
volcano growth Slide 36 Slide 37 Trace elements and isotopic ratios
are generally correlated with variations in SiO 2 content (Kurz et
al, 2003) Slide 38 What if the length scales of compositional
heterogeneities are small?
