  Carbonaceous chondrites (CCs) may have been the carriers of water, volatile
and moderately volatile elements to Earth. Investigating the abundances of
these elements, their relative volatility, and isotopes of state-change tracer
elements such as Zn, and linking these observations to water contents, provide
vital information on the processes that govern the abundances and isotopic
signatures of these species in CCs and other planetary bodies. Here we report
Zn isotopic data for 28 CCs (20 CM, 6 CR, 1 C2-ung, and 1 CV3), as well as
trace element data for Zn, In, Sn, Tl, Pb, and Bi in 16 samples (8 CM, 6 CR, 1
C2-ung, and 1 CV3), that display a range of elemental abundances from
case-normative to intensely depleted. We use these data, water content data
from literature and Zn isotopes to investigate volatile depletions and to
discern between closed and open system heating. Trace element data have been
used to construct relative volatility scales among the elements for the CM and
CR chondrites. From least volatile to most, the scale in CM chondrites is
Pb-Sn-Bi-In-Zn-Tl, and for CR chondrites it is Tl-Zn-Sn-Pb-Bi-In. These
observations suggest that heated CM and CR chondrites underwent volatile loss
under different conditions to one another and to that of the solar nebula, e.g.
differing oxygen fugacities. Furthermore, the most water and volatile depleted
samples are highly enriched in the heavy isotopes of Zn. Taken together, these
lines of evidence strongly indicate that heated CM and CR chondrites incurred
open system heating, stripping them of water and volatiles concomitantly,
during post-accretionary shock impact(s).
