Magma Oceans in the Inner Solar System Linda T. Elkins-Tanton

Magma Oceans Planetecimals accreted first 1.5M.A. of Solar System Gottfried Wilhelm Leibniz : Suggested Earth began as a uniform liquid and differentiated as it cooled Georges-Louis Leclrec, Comte de Buffon: Planets began in the molten state after fragmented from the sun Harold Urey: Silicate and Metal Materials in terrestrial planets melted several times before reaching their final solid state 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 crystallization Compressed crystallization age (Zircons) 182 W and 142 Nd contents of crustal and mantle rocks suggest early core formation Siderophile 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 moon KREEP ( Potassium, Rare Earth Elements, Phosphorus) basalts and picritic glasses enriched in incompatible elements consistant with fractional solidification of a Magma ocean Magma 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 oceans Preservation of Rb-Sr isochrons and W & Nd anomalies suggest little to no crustal recycling Earth: Siderophile content of mantle settled during core segregation at 27GPa and 2000C 142 Nd/ 144 Nd ratio of chondrites differs from earth’s mantle Possible untapped mantle source to balance to chondritic composition Original Crust recycled due to plate tectonics

Vesta HEDs ( Howardite, Eucrites, Diogenites) inferred to originate from vesta Isotopes indicate igneous rocks in first 10 Ma of SS Ages of iron meteorites of destroyed planitecimals Suggest planitecimal formation and differentiation Sources accreted quickly and melted internally Internal Magma Ocean suggested

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 crust Atmosphere initially insulate magma ocean above liquidus and solidus during the solidification Magma oceans with 100ppm water retain free liquid magma ocean surface to prevent quenching Dense 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  SiO 2 ~41-46%, MgO ~30-40%, FeO ~8-18% others 3-6%  Mars is more iron rich  Mafic 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  SiO 2 ~41-46%, MgO ~30-40%, FeO ~8-18% others 3-6%  Mars is more iron rich  Mafic 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 chondrites Volatiles thought to have been released to space upon eucritic volcanic eruptions Un-melted crusts retain near original water content Could obtain higher water contents via fluid fluxes from interior Crystallization of magma ocean facilitates concentration of volatiles in the melt