An oxygen isotope dichotomy in CM2 chondritic carbonates-A SIMS approach

作者：Tyra M A^*; Farquhar J; Guan Y; Leshin L A

来源：Geochimica et Cosmochimica Acta, 2012, 77: 383-395.

DOI：10.1016/j.gca.2011.10.003

We present petrologic and Secondary Ion Mass Spectrometry (SIMS) oxygen isotope analyses of Ca-carbonate within a group of paired Antarctic CM2 chondrites. The carbonates can be grouped into two isotopically and morphologically distinct populations. Type 1 grains (small matrix grains) possess average delta O-18 of 33.7 perpendicular to 2.3 parts per thousand (1 sigma) and average Delta O-17 of -0.81 parts per thousand +/- 0.90 parts per thousand (1 sigma). Type 2 grains (calcite aggregates) possess distinct oxygen isotopic compositions, average delta O-18 of 19.4 parts per thousand +/- 1.5 parts per thousand (1 sigma) and average Delta O-17 of -1.98 +/- 0.9 parts per thousand (1 sigma). These differences are interpreted to indicate that the two populations of calcite formed under different conditions at different times. The carbonates have textural features that suggest an extraterrestrial origin. The data presented here fall within error of a previously measured array for carbonates from CM falls (Benedix et al., 2003). The presence of two generations of carbonate suggests carbonate formation in two discrete events on the parent body of these meteorites. The oxygen isotopic data presented here deviate from prior bulk carbonate measurements undertaken for these meteorites. Most likely, this deviation is because bulk carbonate analyses included vein carbonate which formed during terrestrial weathering.

• 出版日期2012-1-15