Analytical uncertainties were calculated as the standard error of the mean, but if the mean square weighted deviates (MSWD or reduced chi-squared statistic) was greater than one, the analytical uncertainty was inflated by multiplying the standard error of the mean by the square-root of the MSWD. All samples analysed in this study (including NWA 5790) have plateau and weighted-mean ages with MSWD of less than two, and probability of fit (“p”) values of greater than 0.05 (95% confidence), indicating the analyses are statistically robust Ar trapped component—the most precise constraint yet obtained for the mid-Amazonian atmosphere of Mars. The red star in the Elysium region marks the location of a potential source crater for the nakhlites.b Relative characteristics of terrestrial and Martian plume volcanism.The augite crystals (deep blue, in a, e, i) are often zoned, with an outer rim of ferroan pigeonite.Olivine crystals are also present, but less common. The mesostasis also contains crystals of titanomagnetite (Tmag), iron sulphide (Fe, S) and chlorine-bearing apatite.Images from the other meteorites (MIL 03346, Yamato 000593 and Yamato 000749) are in Supplementary Fig. Panels a, e, i display the distribution of aluminium (brown), iron (green) and magnesium (blue); panels b, f, j show potassium (red); panels c, g, k illustrate the distribution of phosphorus (blue, concentrated in apatite) and sulphur (magenta, in iron sulphide), as well as the backscattered electron intensity in grey; and panels d, h, l show the distribution of chlorine (green, in apatite).
Three aliquots (Lafayette aliquot 02, MIL 03346 aliquot 2 and Yamato 000593 aliquot 3) yielded plateau segments containing between 52 and 59% Ar released, we are confident that these three aliquots also record eruption ages. Two of the three aliquots, however, yielded 11 and 13 contiguous steps (ca. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
The top panel of each sample represents the portion of radiogenic Ar (Ar released; these results therefore provide only a minimum age constraint for the eruption of this sample.
Additional aliquots from these meteorites (n = 2 to 5) are highly reproducible, with similar degassing spectra and concordant plateau ages (Supplementary Figure 2)The eruption age for each meteorite was calculated as a weighted-mean of all plateau steps.
Here we quantify the growth rate of a Martian volcano by Ar and cosmogenic exposure dating of six nakhlites, meteorites that were ejected from Mars by a single impact event at 10.7 ± 0.8 Ma (2σ).
We find that the nakhlites sample a layered volcanic sequence with at least four discrete eruptive events spanning 93 ± 12 Ma (1416 ± 7 Ma to 1322 ± 10 Ma (2σ)).