Thermal metamorphism of primitive meteorites—V. Ten trace elements in Tieschitz H3 chondrite heated at 400–1000°C

Abstract

We determined ten trace elements by neutron activation analysis in Tieschitz (H3) chondrite powder heated in a low-pressure environment (initially ~ 10 −5 atm H 2) for 1 week at 100°C increments from 400–1000°C. Of these, Co seems unaffected by heating, 20% of Ga is lost only at 1000°C and losses of other elements progress with temperature to extremes of 25% for Se, 75% for Cs and 90–97% for Ag, Bi, In, Te, Tl and Zn. Treating elemental mobilization as kinetically-controlled by diffusion from spherical grains of uniform size, Ag, Cs, In and Se are lost from a single site by a single process while Bi, Te, Tl and Zn are lost from two sites or from one site by different processes at high and low temperatures. Magnitudes of apparent activation energies for loss of the first four elements at all temperatures and the last four at low temperatures are consistent with volume diffusion; at high temperatures Bi, Te, Tl and Zn are lost by a low-energy process, like desorption. We compared trace element abundances, patterns of statistically-significant correlations, factor analysis and two-element correlations between Tieschitz and heated Krymka (L3) and, except for factor analysis, “as-received” H3–6 chondrites. Trends for heated ordinary chondrites are similar though small differences occur; those for Tieschitz and H3–6 chondrites differ markedly indicating that H3–6 chondrites—unlike E3–6 chondrites—probably escaped substantial open-system metamorphism. Sharp contrasts in pictures for E-, L- and H-group chondrites indicate substantial differences in genetic histories.