Start Dating pulse

Dating pulse

Although their size and impact crater density indicate continued activity over billions of years, their formation rates are poorly understood.

The weighted mean cosmogenic exposure age is 10.7 ± 0.8 Ma (2σ, full external uncertainty, bold text and grey shaded area), which represents the timing of the nakhlite impact event on Mars Ar component.

These images illustrate that the nakhlite meteorites are igneous rocks, dominated by euhedral augite crystals set in a fine-grained mesostasis.

The augite crystals (deep blue, in a, e, i) are often zoned, with an outer rim of ferroan pigeonite.

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).

A small proportion of terrestrial volcanoes are fed by mantle plumes—highly localized upwellings of abnormally hot rock that ascend from deep within the mantle and undergo partial melting at relatively shallow depths) are located in the Tharsis and Elysium regions, with the largest volcano, the 600 km wide Olympus Mons, rising more than 21 km above the surrounding plains.

The red star in the Elysium region marks the location of a potential source crater for the nakhlites.

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.