Shock-Induced Volatile Loss from a Carbonaceous Chondrite: Implications for Planetary Accretion

Solid recovery impact-induced volatile loss experiments on the Murchison C2M meteorite indicate that for an impact of a given velocity, H2O and total volatiles are driven from the sample in the same proportion as present initially. Thus, the primitive surface volatile budget (volatiles reacted with the solid surface plus atmosphere) of a planet growing by accretion would have the same bulk elemental composition as the volatiles in the incident planetesimals. Incipient devolatilization of Murchison occurs at an initial shock pressure of about 11 GPa and complete devolatilization occurs at a pressure of about 30 GPa. For the Earth, incipient and complete devolatilization of accreting planetesimals would occur when the planet reached approximately 12% and 27%, respectively, of its present-day radius. Thus, impact-induced devolatilization would profoundly affect the volatile distribution within the accreting planet. Prior to metallic core formation and internal differentiation the growing planet would have a very small core with the same volatile content as the incident material, a volatile depleted 'mantle', and an extremely volatile rich surface. In the case of the Earth, 99.4 wt% of the total incident volatile material would end up on or near the planetary surface. i a. -x .-.. ''--' •now at Department of Geology, Arizona State University, Tempe, AZ 85287 https://ntrs.nasa.gov/search.jsp?R=19860012007 2017-09-12T19:27:24+00:00Z