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The Source Crater of Martian Shergottite Meteorites

Science  21 Mar 2014:
Vol. 343, Issue 6177, pp. 1343-1346
DOI: 10.1126/science.1247282

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Sourcing Martian Meteorites

There are nearly 150 recognized martian meteorites, but where exactly they came from on Mars is not known. Werner et al. (p. 1343, published online 6 March) present evidence that the <5 million-year-old Mojave impact crater on Mars is the single ejection site of one type of martian meteorites: the shergottites. The Mojave crater formed on an ancient terrain on Mars, and so the shergottites represent old martian crustal material.

Abstract

Absolute ages for planetary surfaces are often inferred by crater densities and only indirectly constrained by the ages of meteorites. We show that the <5 million-year-old and 55-km-wide Mojave Crater on Mars is the ejection source for the meteorites classified as shergottites. Shergottites and this crater are linked by their coinciding meteorite ejection ages and the crater formation age and by mineralogical constraints. Because Mojave formed on 4.3 billion–year-old terrain, the original crystallization ages of shergottites are old, as inferred by Pb-Pb isotope ratios, and the much-quoted shergottite ages of <600 million years are due to resetting. Thus, the cratering-based age determination method for Mars is now calibrated in situ, and it shifts the absolute age of the oldest terrains on Mars backward by 200 million years.

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