Taking the pulse of Mars via dating of a plume-fed volcano

Abstract

Mars hosts the solar system's largest volcanoes. Although their size and impact crater density indicate continued activity over billions of years, their formation rates are poorly understood. Here we quantify the growth rate of a Martian volcano by ⁴⁰Ar/³⁹Ar 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)). A non-radiogenic trapped ⁴⁰Ar/³⁶Ar value of 1511 ± 74 (2σ) provides a precise and robust constraint for the mid-Amazonian Martian atmosphere. Our data show that the nakhlite-source volcano grew at a rate of ca. 0.4-0.7 m Ma^-1-three orders of magnitude slower than comparable volcanoes on Earth, and necessitating that Mars was far more volcanically active earlier in its history.Mars hosts the solar system's largest volcanoes, but their formation rates remain poorly constrained. Here, the authors have measured the crystallization and ejection ages of meteorites from a Martian volcano and find that its growth rate was much slower than analogous volcanoes on Earth.

Fig. 1

Distribution and size of Martian volcanoes. a Amazonian volcanic products on Mars (digital elevation model and orange outlines ) 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. 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. Data and references in Supplementary Table 1

Fig. 2

Petrology of nakhlite meteorites. 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. 1. 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). 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. Olivine crystals are also present, but less common. Potassium is concentrated in mesostasis feldspar. The mesostasis also contains crystals of titanomagnetite (Tmag), iron sulphide (Fe,S) and chlorine-bearing apatite. As potassium and chlorine are both dominantly hosted in the mesostasis, the argon gas derived from radiogenic decay of potassium and chlorine gas from apatite will be closely associated in location and thermal behaviour during a ⁴⁰Ar/³⁹Ar experiment, and the contribution from chlorine must therefore be accounted for during the cosmogenic argon correction procedure

Fig. 3

Cosmogenic exposure dates for the nakhlites. ³⁸Ar cosmogenic exposure ages overlap within uncertainty, which is consistent with all of the nakhlites being sourced from the same impact. Blue data points were analysed at Lawrence Livermore, and red data points were analysed at SUERC. 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

Fig. 4

Trapped Martian ⁴⁰Ar/³⁶Ar at the time of nakhlite formation. Isochron analysis of a Lafayette and b Yamato 000593 reveal the composition of initial trapped ⁴⁰Ar/³⁶Ar component. All symbols and results are reported at the two-sigma level. Blue ellipses denote plateau steps that were included in the isochron regression, white ellipses are outliers from the low-temperature steps that were excluded from the isochron analysis, and the red lines indicate the 2σ uncertainty envelope

Fig. 5

Representative ⁴⁰Ar/³⁹Ar age spectra for the nakhlites. Samples are arranged in chronologic order from youngest to oldest: a Lafayette aliquot 01, b Yamato 000593 aliquot 02, c NWA 5790 aliquot 02, d Nakhla aliquot 01, e Miller Range 03346 aliquot 03 and f Yamato 000749 aliquot 01. The top panel of each sample represents the portion of radiogenic Ar (⁴⁰Ar*) released from each degassing step; the middle panel represents the K/Ca value for each step; and the lower (main) panel shows the calculated ⁴⁰Ar/³⁹Ar age for each degassing step. All uncertainties are 2σ. The nakhlites yield excellent results, often with statistically robust plateaus comprising >90% of the ³⁹Ar released. NWA 5790 c is an exception, with concordant steps spanning only 34% of the ³⁹Ar 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)

Fig. 6

Stratigraphic model for the nakhlite meteorites. a Summary of ⁴⁰Ar/³⁹Ar age data. Each meteorite has multiple aliquots with highly reproducible plateau ages (red squares). Bold black squares and horizontal grey bars represent weighted mean ages. The ⁴⁰Ar/³⁹Ar results indicate that the nakhlites were erupted in at least four temporally discrete eruptions, with volcanic activity spanning 93 ± 12 Ma. All uncertainties are 2σ. b Schematic cross-section for a layered lava flow sequence, with nakhlite stratigraphic relationships and outline of post-impact structure

Fig. 7

A potential nakhlite source crater. This crater is located on the Elysium lava plains, to the northwest of the Elysium shield volcano on Mars, at 130.799°E, 29.674°N (Fig. 1). a Overview of the crater, which is 6.5 km in diameter, large enough to have ejected Martian rocks towards Earth. THEMIS image V13713007, Band 3, NASA/ASU. Black rectangles indicate the locations for subsequent images. b–d Detail of the northwestern, northeastern and southern crater rim, respectively, representing parts of HiRISE image ESP 017997_2100, NASA/JPL/University of Arizona. These images show numerous sub-horizontal layers, which are interpreted as lava flows (e.g., ref. for similar features elsewhere on Mars). White arrows indicate prominent layers; see inset for detailed view. Solar illumination is from the west in all images