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Buseck Center for Meteorite Studies

New paper on CR chondrite metamorphism

In a new paper published in Geochimica et Cosmochimica Acta, Center Assistant Research Scientist Dr. Jemma Davidson and co-authors report on one of the most pristine carbonaceous chondrites found to date.

By utilizing the chromium content of iron-rich olivine in two Renazzo-like (CR) chondrites from Antarctica, Davidson and co-authors re-examine the metamorphic trend for the CR chondrite group. Their analyses indicate that, contrary to pre-existing assumptions, this method is only appropriate for identifying metamorphic endmembers (i.e., those that have experienced little or significant heating on their parent asteroid).

Based on their findings, Miller Range 090657 appears to be one of the most pristine CR chondrites analyzed to date, while Graves Nunataks 06100 is the most shock-heated CR chondrite known.

Davidson and co-authors also demonstrate the utility of combining bulk isotopic compositions with petrographic characteristics for determining the relative pristinity/heating of low petrographic type chondrites.

“Utliizing the many analytical techniques that are available to us – and correlating those results with one another – is essential for identifying the least altered astromaterials,” says Davidson. “If we want to understand how our Solar System evolved to its current state, we need to determine the nature of the starting material. Pristine chondrites like Miller Range 090657 provide a great opportunity to do that.”

This study is part of Dr. Davidson’s ongoing work aimed at identifying the most pristine extraterrestrial samples in order to characterize the materials from which our Solar System formed and understand how this material evolved over the last four and a half billion years.

Read the full paper here, free to download until Nov 30!

Davidson J., Schrader D. L., Alexander C. M. O’D., Nittler L. R., and Bowden R. (2019) Re-examining thermal metamorphism of the Renazzo-like (CR) carbonaceous chondrites: Insights from pristine Miller Range 090657 and shock-heated Graves Nunataks 06100. Geochimica et Cosmochimica Acta 264: 240-256.