The onset of silicate melting in planetesimals: experimental constraints on the formation of ureilites, primitive achondrites and Si-rich achondrites.

Within a few million years of the formation of the solar system, early-formed planetesimals, heated by the radioactive decay of 26Al, reached internal temperatures sufficient to melt. Primitive achondrites and ureilites are meteorites that sample the rocky mantle of several such planetesimals. Their chondritic source material lost variable amounts of silicate melts and sulfur-rich metal melts but the melting process was interrupted before the formation of magma oceans. I will present high temperature experiments (1060-1250 ºC) detailing those early igneous processes.

The main groups of primitive achondrites and ureilites have in common that their precursor material contained high concentrations of alkali elements (Na+K). The ureilite parent body was not enriched in refractory elements contrary to some groups of chondrites (e.g. CM and CV) that were once thought to be closely related to ureilites. The melting of alkali-rich chondritic material produced abundant Si-rich and Al-rich magmas that have been occasionally preserved and sampled as “Si-rich achondrites”. Those results, together with nucleosynthetic isotope anomalies analyzed in ureilites, suggest that the inner part of the protoplanetary disk where ureilites formed was not significantly depleted in Na and other “moderately volatile” elements.

About this Series

The Chemical Oceanography, Geology, Geochemistry, and Geobiology Seminar [COG³] is a student-run seminar series. Topics include chemical oceanography, geology, geochemistry, and geobiology. The seminars take place on Fridays from 10-11am in Building E25, Room 119, unless otherwise noted (term-time only). 2016/2017 co-ordinators: Sharon Newman (sanewman@mit.edu), Ben Klein (bzklein@mit.edu), Christopher Kinsley (ckinsley@mit.edu), Max Collinet (collinet@mit.edu).