Pulse speed dating
The chlorine-derived isotopes are a particular issue for the nakhlite group of Martian meteorites, which can contain over 1000 ppm Cl hosted in salts and/or chlorine-bearing apatite that can be found in the meteorite's mesostasis (Fig. Panels a–d are scanning-electron microscope images of Nakhla; e–h are from Lafayette, and i–l show a representative area of NWA 5790.
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).
b Relative characteristics of terrestrial and Martian plume volcanism.
In comparison to terrestrial volcanoes (blue) those on Mars (red) have a greater volume and duration, but much lower eruption rates.
The nakhlites comprise 18 meteorites (not accounting for pairing).
Their bulk chemistry is basaltic, with abundant clinopyroxene, less common olivine and a rapidly quenched fine-grained mesostasis comprising feldspar and accessory phases, including chlorapatite and volcanic glass, replicate geochronological analyses of the same meteorite disagree; many ages are imprecise and/or fail the robust criteria that define statistical significance (Supplementary Table 2).
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.
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).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. This value is more precise than, but within analytical uncertainty of, measurements by the Curiosity rover for the present-day Martian atmosphere (1900 ± 600, 2σ)Ar ages show the nakhlites were erupted between 1416 ± ± 10 Ma (2σ, i.e., mid-Amazonian), a period spanning 93 ± 12 Ma (Table 1 and Fig. Our interpretation is that the nakhlites have sampled a layered volcanic sequence, with the Ar ages defining stratigraphic position (Fig. Two sets of meteorites (respectively: Nakhla and MIL 03346; NWA 5790 and Yamato 000583) are not temporally resolvable at the 2σ level (Fig. 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. 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.