77th Annual Meteoritical Society Meeting (2014) 5062.pdf

MOJAVE CRATER, MARS, THE SHERGOTTITES’ SOURCE CRATER AND CHRONOLOGY MODELS. S.C. Werner1, A. Ody2, and F. Poulet3. 1CEED, University of Os- lo, Norway, [email protected] 2LGT, Université de Lyon 1 France. 3 IAS, Université Paris Sud 11, France.

Introduction: Absolute ages for planetary surfaces are often inferred by crater densities, and are only indirectly constrained by ages of meteorites. Cratering chronology models are calibrated based on lunar samples, and are transferred towards other planets using crater scaling laws and cratering rate ratios. This transfer often relies on extrapolations. We have shown that the <5 Myrs old and 55-km wide Mojave Crater is the ejection source for the meteorites classified as shergottites [1], and thus allows the cali- bration of the chronology model of Mars. The Link: Shergottites and this crater are linked by their co- inciding meteorite ejection ages and the crater formation age, and mineralogical constraints [1]. The Calibration: Thus, the cratering-based age determina- tion method for Mars is now calibrated. Our new Martian crater- ing chronology model is tested against the in situ determined ra- diometric and exposure ages for a mudstone in Gale crater [3], and the ages found with both methods are identical. Implications: Because Mojave formed on 4.3 Gyrs old ter- rain, the original crystallization ages of shergottites are old, as inferred by Pb-Pb isotope ratios [4-6], and the much-quoted <600 Myrs shergottite ages [e.g., 7] are due to resetting. Martian sur- face features dated with cratering statistics shifts the absolute age of the oldest terrains of Mars backwards by 200 Myrs. References: [1] Werner, S. C., Ody, A. and Poulet, F., 2014, Science 343, 1343-1346. [2] Herzog, G. F. and Caffee, M. W. in Treatise on Geochemistry, Turekian and Holland, Eds. (Elsevier, Amsterdam, Netherlands, ed. 2, 2013), 1, 419–454. [3] Farley, K. et al. 2014 Science 343, 1247166-1-5. [4] Bouvier, A., Blichert- Toft, J. and Albarède, F. 2009, Earth Planet. Sci. Lett. 280, 285– 295. [5] Bouvier, A., Blichert-Toft, J., Vervoort, J. D., Albarède, F., 2005, Earth Planet. Sci. Lett. 240, 221–233. [6] Bouvier A. et al., 2013, Lunar Planet. Sci. Conf. XLIV, abstr. 2421. [7] Nyquist, L. E. et al.,2001, Space Sci. Rev. 96, 105–164.