The Lodran primitive achondrite: petrogenetic insights from electron and ion microprobe analysis of olivine and orthopyroxene

• Published in: Geochimica et cosmochimica acta Vol. 59; no. 14; pp. 3061 - 3070
• Main Authors: Papike, J.J., Spilde, M.N., Fowler, G.W., Layne, G.D., Shearer, C.K.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.1995
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/0016-7037(95)00195-6

The Lodran primitive achondrite is thought to represent some of the earliest events in the differentiation of chondritic asteroids. Most researchers who studied Lodran believe that it is a restite from which a melt, enriched in the incompatible trace and minor elements, was extracted. This process is reflected by a lack of feldspar in the Lodran mineral assemblage. Presumably, after or during melting, a reduction event took place resulting in an increase in Mg/Fe near the rims of both olivine and orthopyroxene. The reduction process is far more advanced in olivine than in pyroxene because of the more rapid Fe-Mg diffusion rates in olivine. Narrow reaction rims (<10 μm) around orthopyroxene grains show a depletion in Ca, Al, Cr, Ti, REEs, and Y and an increase in Mg (reverse zoning). These systematics are largely the result of melting and to a lesser extent of reduction. Significant reaction of olivine has taken place by reduction and/or sulfidatuon and to a lesser extent by melting. This is reflected by a decrease in Fe, Co, and Ni and an increase in Mg towards the rims of olivine. The reactions by which reduction and/or sulfidation of olivine took place are not confirmed. However, the following represent two possible reactions: ▪