46 Chapter 2 TEMPERATURES OF AQUEOUS ALTERATION ON CARBONACEOUS CHONDRITE PARENT BODIES

• Main Authors: Weifu Guo, Michael Zolensky, John M. Eiler
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Tagish; Tagish Lake
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.425.304; http://thesis.library.caltech.edu/5058/5/05Chapter2.pdf

Application of stepped phosphoric acid digestion and carbonate clumped isotope thermometry to carbonates in carbonaceous chondrites ⎯ GRO 95577 (CR1), Orgueil (CI) and Tagish Lake (ungrouped C2) ⎯ indicates that aqueous alterations on carbonaceous chondrite parent bodies occurred from-31 to 65˚C from fluids with δ 18 OVSMOW values of-29.7 ‰ to 11.8 ‰ and δ 17 OVSMOW of-14.9 ‰ to 7.6‰. The estimated carbonate formation temperatures decrease in the order: calcite> dolomite> breunnerite. Based on independent constraints on the ages of these carbonates and models of the evolution of the oxygen isotope compositions of parent body waters, this trend indicates that the parent bodies were cooling as the aqueous alteration proceeded. We estimate that aqueous alteration on the carbonaceous chondrite parent bodies started within 1-2 million years after the accretion of those parent bodies, and that the alteration temperatures decreased from 34˚C to 18˚C in the first ~4 million years and further to-20˚C after a total of ~6.5 million years. Our results provide the first direct measurements of the low-temperature cooling histories of C1 and C2 carbonaceous chondrite parent bodies. 1.