Titanum distribution in enstatite chondrites and achondrites, and its bearing on their origin

Abstract

Titanium, a strongly lithophilic element in terrestrial rocks and most meteorites, is predominantly chalcophilic in the highly-reduced enstatite chondrites and enstatite achondrites. There it occurs as a constituent of troilite (max. 0.95 wt. % in enstatite chondrites; max. 16 wt. % in enstatite achondrites), daubreelite (max. 0.12 wt. % in enstatite chondrites), ferroan alabandite (max. 0.04 wt. % in enstatite chondrites; max. 0.10 wt. % in enstatite achondrites), niningerite (max. 0.09 wt. % in enstatite chondrites), and of oldhamite (max. 0.02 wt. % in enstatite chondrites). Titanium is a major constituent of a new sulfide mineral, a titanium-iron sulfide withTi>Fe, which occurs in the Bustee enstatite achondrite. The element may also combine with nitrogen to form TiN (osbornite), a mineral found in the Bustee and Khor Temiki enstatite achondrites. On the basis of similar bulk titanium contents but strikingly different troilite contents and titanium concentrations in troilite of enstatite chondrites and enstatite achondrites, it is concluded that enstatite achondrites are not directly genetically related to enstatite chondrites; i.e. melting of enstatite chondrites with gravitational differentiation cannot account for the origin of enstatite achondrites. All that can be said is that enstatite chondrites and enstatite achondrites were formed under similar highly-reducing conditions.