Earth’s InteriorChapter 19Major Parts• Crust (Above the Moho)– Oceanic (8 to 10 km of basalt & gabbro)– Continental (30 to 60 km of granite)• Mantle - Moho to 2900 km - Solid Rock– Upper (Moho to 410km) (Olivine + pyroxene)– Transition Zone (410 -670 km) (Silicate Spinels)– Lower 670 to 2900 km (Perovskite + periclase)• Core (2900 to 6367km)– Outer Core (Liquid Metal)– Inner Core (Solid Metal)Earth’sInteriorCrust• Oceanic Crust (Basalt and Gabbro)– Thin (8 - 10 km)– Dense (2.9 - 3.1 g/cm3)– Young (< 250 my)• Continental Crust (Granite + Diorite + Seds)– Thick (30 - 60 km)– Light (2.7 - 2.8 g/cm3)– Old (250 - 4000 my)Mantle• Upper Mantle (Moho to 410 km)– Peridotite (Olivine + pyroxene)– Eclogite (Pyroxene + Garnet)• Transition Zone (410 - 670 km)– Spinels and Spinelloids• Lower Mantle (670 - 2900 km)–MgSiO3 - Perovskite– MgO - PericlaseCore• Outer Core (2900 to 5150km)– Molten iron metal (+ ~10% lighter element)– No S-wave transmission• Inner Core (%150 - 6378 km)– Solid Iron Metal– May slowly rotate relative to mantleHow do we know what’s there?• Seismology– S-wave shadow– P and S reflections and conversions• Meteorites:– Earth formed from primitive meteorites• Xenoliths from kimberlites & basalts• ExperimentsSeismology• S-wave shadow– No S-waves opposite-side earthquakes– Core (outer) must be molten• P and S reflections– Discontinuities at 410 and 670 km– Phase Changes• P and S travel time anomalies– Tomography– Hot and cold regionsXenoliths• Xenoliths are ‘strange rocks’• Xenoliths are inclusions in kimberlites and basalts• Xenoliths provide natural high pressure rocks.– Kimberlites bring diamonds and other rock samplesfrom as deep as 670 km.– Basalts are derived from the lithospheric mantleMeteorites• Meteorites tell us of Earth’s bulk composition– Chondrites are primitive meteorites– Earth is “chondritic”• Composition is similar to sun minus H, Heand other volatiles.Experiments• Multi-Anvil Press– Synthesis experiments to 1000 km depth– Samples 1-5 mm3• Diamond Anvil Cell– Spectroscopy– Ultrasound– X-ray diffractionConvection in solid mantle• Driven by U, Th, K decay (internal engine)• Moves about 2 cm/yr• Causes earthquakes• Move plates• Splits and rejoins continents• One Cell or two?Magnetic Field• Due to electrical currents from Earth’s dynamo.• Convection in liquid metal outer core.• Convection is coupled to Earths rotation.• Field is subject to sporadic reversals.– Last reversal was 30,000 years ago.• Field hold ozone layer (UV shield) in
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