Magma Oceans in the Inner Solar System Linda T Elkins Tanton Magma Oceans Planetecimals accreted first 15MA of Solar System 1694 Gottfried Wilhelm Leibniz Suggested Earth began as a uniform liquid and differentiated as it cooled ID: 764041
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Magma Oceans in the Inner Solar System Linda T. Elkins- Tanton
Magma Oceans Planetecimals accreted first 1.5M.A. of Solar System 1694- Gottfried Wilhelm Leibniz : Suggested Earth began as a uniform liquid and differentiated as it cooled 1748- Georges-Louis Leclrec, Comte de Buffon: Planets began in the molten state after fragmented from the sun1955- Harold Urey: Silicate and Metal Materials in terrestrial planets melted several times before reaching their final solid state1992- Taylor & Norman: Define Magma oceans by 2 criteria a) magma behaves as liquid with small crystal fraction b) magma consists of a substantial fraction of parent body
Magma Oceans Model: Core formation Early and crustal formation by 4.4Ga as evidenced by: Some compositions and mineralogy suggest early widespread melting and fractional crystallizationCompressed crystallization age (Zircons)182W and 142Nd contents of crustal and mantle rocks suggest early core formationSiderophile content of the mantle is thought to be due to core formation and accretion
The Moon Apollo Missions: Provoked magma ocean in current form due to discovery of anorthosites suggesting floatation on magma ocean of early moonKREEP ( Potassium, Rare Earth Elements, Phosphorus) basalts and picritic glasses enriched in incompatible elements consistant with fractional solidification of a Magma oceanMagma ocean was originally ~100s km deep as evidenced by Europium deficits on Mare basalts and enrichment in Anorthitic crust
Mars and Earth Mars: Early core formation suggests accretionary heat concentrated in brief time period giving greater melting potential core formation enhanced by presence of magma oceansPreservation of Rb-Sr isochrons and W & Nd anomalies suggest little to no crustal recyclingEarth:Siderophile content of mantle settled during core segregation at 27GPa and 2000C142Nd/144Nd ratio of chondrites differs from earth’s mantlePossible untapped mantle source to balance to chondritic compositionOriginal Crust recycled due to plate tectonics
Vesta HEDs ( Howardite , Eucrites, Diogenites) inferred to originate from vestaIsotopes indicate igneous rocks in first 10 Ma of SSAges of iron meteorites of destroyed planitecimals Suggest planitecimal formation and differentiationSources accreted quickly and melted internallyInternal Magma Ocean suggestedhttp://www.nasa.gov/mission_pages/dawn/multimedia/pia15678.html
Primary Crust formation Conductive lids on magma oceans formed one of the following ways: Internal magma oceans- outer portion of planetecimal may remain un-melted and conductive (eg. Vesta)Buoyant phases may form in the magma ocean and float to the surface ( eg. Plagioclase on moon)Mafic silicate magma may quench to form solid crustAtmosphere initially insulate magma ocean above liquidus and solidus during the solidificationMagma oceans with 100ppm water retain free liquid magma ocean surface to prevent quenchingDense quenched material sinks
Jeff Plescia 2008
Cooling of Magma Ocean
Crystal settling and Entrainment Oxides ( SiO2, Al2O3, MgO , FeO, and CaO) make 97 wt% of total silicates in terrestrial planets SiO2 ~41-46%, MgO ~30-40%, FeO ~8-18% others 3-6%Mars is more iron richMafic phases (Olivine and Pyroxine) are denser and sink
Crystal settling and Entrainment Oxides ( SiO2, Al2O3, MgO , FeO, and CaO) make 97 wt% of total silicates in terrestrial planets SiO2 ~41-46%, MgO ~30-40%, FeO ~8-18% others 3-6%Mars is more iron richMafic phases (Olivine and Pyroxine) are denser and sink
Effect of volatiles on Magma Ocean With added volatiles
Volatile behavior Abundance and distribution of Carbon and Hydroxyl determine mantle viscosity and melting temperature Eucrites , such as ones in Vesta, lower in volatiles than chondritesVolatiles thought to have been released to space upon eucritic volcanic eruptionsUn-melted crusts retain near original water contentCould obtain higher water contents via fluid fluxes from interiorCrystallization of magma ocean facilitates concentration of volatiles in the melt