G. Quitte

Early Archean serpentine mud volcanoes at Isua, Greenland, as a niche for early life

The Isua Supracrustal Belt, Greenland, of Early Archean age (3.81–3.70 Ga) represents the oldest crustal segment on Earth. Its complex lithology comprises an ophiolite-like unit and volcanic rocks reminiscent of boninites, which tie Isua supracrustals to an island arc environment. We here present zinc (Zn) isotope compositions measured on serpentinites and other rocks from the Isua supracrustal sequence and on serpentinites from modern ophiolites, midocean ridges, and the Mariana forearc. In stark contrast to modern midocean ridge and ophiolite serpentinites, Zn in Isua and Mariana serpentinites is markedly depleted in heavy isotopes with respect to the igneous average. Based on recent results of Zn isotope fractionation between coexisting species in solution, the Isua serpentinites were permeated by carbonate-rich, high-pH hydrothermal solutions at medium temperature (100–300 °C). Zinc isotopes therefore stand out as a pH meter for fossil hydrothermal solutions. The geochemical features of the Isua fluids resemble the interstitial fluids sampled in the mud volcano serpentinites of the Mariana forearc. The reduced character and the high pH inferred for these fluids make Archean serpentine mud volcanoes a particularly favorable setting for the early stabilization of amino acids.

Correlated Iron 60, Nickel 62, and Zirconium 96 in Refractory Inclusions and the Origin of the Solar System

We report precise nickel isotopic compositions, measured with high-resolution MC-ICPMS, for calcium-aluminum-rich inclusions (CAIs) considered to be the earliest objects formed in the solar system. The CAIs display correlated anomalies of 60Ni and 62Ni, possibly coupled with effects on 96Zr. This is not predicted from stellar production models unless the 60Ni results from the decay of 60Fe. The effects show the signature of neutron-burst nucleosynthesis in a massive star. Such a neutron burst is plausibly responsible for the abundance of many of the short-lived radioactivities present in the early solar system; therefore, at least some of the nucleosynthetic heterogeneity previously reported from CAIs, leached carbonaceous chondrites, and presolar grains is likely to have been generated by dust injection from a supernova at a time close to the beginning of the solar system, which is consistent with a trigger for solar nebula collapse, or generated directly by dust injection into the protoplanetary disk.

Quantitative extraction and high precision isotope measurements of nickel by MC-ICPMS

This paper presents a new technique for the precise and accurate determination of Ni isotopic composition in geological samples, involving a two-stage ion-exchange procedure for nickel extraction and the use of a large-geometry high-resolution MC-ICPMS instrument. The key step of the chemical separation is an ion-exchange procedure based on the complexation of Ni with dimethylglyoxime which replaces the previous liquid–liquid extraction technique. The new method allows for quantitative recovery of Ni even for silicate samples as opposed to the previous technique. Measurements of an Ni standard doped with Fe or Zn show that isobaric interferences of these elements can be accurately corrected as long as Fe/Ni < 0.1 and Zn/Ni < 0.0006. Replicate measurements of a standard solution yield long-term external reproducibilities (2σ) of ±50 ppm for 60Ni/58Ni and ±120 ppm for 61Ni/58Ni, when ratios are normalized to 62Ni/58Ni.