Speaker:M.A. Ivanova – Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academу of Sciences

Title: The first solid material formed in the Solar system

The first solid material formed in the Solar system preserved traces of the earliest chemical and isotopic fractionation in the protoplanetary disk. It is represented by refractory Ca, Al- inclusions (CAIs), amoeboid olivine aggregates (AOAs), and chondrules found in primitive chondrite meteorites. Knowledge about the formation of the first solid material largely depends on accurate chronological data – the time and rate of the transformation of the protoplanetary disk consisting of gas and dust into solid material. Using the 206Pb-207Pb method, the absolute ages of CAIs were determined and based on these ages the average value of the age of the Solar system was obtained. Using the 26Al-26Mg isotope system, the interval of CAIs formation in the protoplanetary disk was confirmed. After accretion on the parent asteroids, the CAIs underwent anaqueous fluid alteration, time of this alteration was determined by the 53Cr-53Mn dating. The CAIs material is very diverse. Inclusions with unusual morphology as well as compound and ultra-refractory CAIs, were found. CAIs in the form of a flat and concave disk have experienced aerodynamic deformation during their movement in the protoplanetary disk.

Compound CAIs indicate the earliest accretion of centimeter-sized bodies. The trapped ultra-refractory inclusions (UR CAIs) retain traces of chemical and isotope fractionation at a higher temperature stage of formation (>1800 K) than usual CAIs; they are enriched in refractory REE and have a heterogeneous oxygen isotope composition which confirms the existence of two oxygen reservoirs – enriched and depleted in the 16O isotope. CAIs of different groups of

chondrites (CV3 and CH-CB types) differ in mineralogy and bulk composition, but there is probably a genetic relationship between them, which was discovered due to the study of the evaporation process of CAIs melts formed during high-energy events.