PPT Slide
Granite (continental crust)
- light-colored rock containing quartz and feldspar
- relatively rich in Si, Na and K
- r (density) is ~2800 kg.m-3
Gabbro (oceanic crust)
- Dark-colored rock, containing feldspar and olivine
- relatively low in Si, Na and K; rich in Ca, Mg (and Fe)
- r is ~2900 kg.m-3
(Upper) MANTLE
- relatively low Si; rich in Mg
- r is ~3300 kg.m-3
rcont.crust/rmantle = 2800/3300 = .85
rocean.crust/rmantle = 2900/3300 = .88
rcont.crust/rocean.crust = 2800/2900 = .97
9 km above sealevel (Mt. Everest; Nepal) tops ~85 km thick continental crust
4 km below sealevel ocean floor underlain by few km thin oceanic crust