The solar systems abundances of phosphorus and titanium and the nebular volatility of phosphorous

Abstract

The bulk chemical composition of Orgueil and 25 other carbonaceous chondrites was determined by x-ray fluorescence analysis. The sample sizes of the analyzed meteorites were in all cases 120 mg. The abundances of P and Ti in Orgueil and Ivuna were precisely determined by the standard addition method. The new P CI abundance is 926 ± 65 ppm. Excluding the low P of Ivuna and one Orgueil sample with unusual chemistry gives a CI P content of 930 ± 23 ppm. A CI abundance of 926 ppm corresponds to a P/Si wt ratio of 8.66 × 10-3 (atomic ratio 7.85 × 10-3). For Ti a CI content of 458 ± 18 ppm and a Ti/Si wt ratio of 4.28 × 10-3 (atomic ratio 2.51 × 10-3) were found. A Si content of 10.69% was obtained for average CI. The new P CI abundance is 20 to 30% below earlier estimates, while the Ti CI abundance is in agreement with earlier determinations. From the results of the analyses of bulk carbonaceous chondrites it is concluded: (1) Refractory element/Mg ratios increase from CI through CM and C3O to C3V, but ratios among A1, Ca and Ti are constant, except for low Ca/A1 ratios in the reduced subgroup of C3V. (2) The Si/Mg ratios are constant in all groups of carbonaceous chondrites. (3) There is a volatility related depletion of Cr and Fe, but the Cr/Fe ratios are constant. (4) The sequence of volatility related depletions of the moderately volatile elements P, Au, As, Mn, and Zn follows condensation temperatures (except for As), if in condensation calculations non-ideal solid solution in the host phase is considered.