Komatiites and picrites generated by high degrees of mantle partial melting are proposed to be probes of the Earth’s deep mantle. Tungsten isotopes offer a rare chance to ascertain early differentiation, late accretion, core-mantle interaction, and subsequent evolution of the Earth’s mantle. Here we present new W isotope data for Archean komatiites and basalts from the Barberton (South Africa) and Suomussalmi (Finland) Greenstone Belts and Permian picrites from the Emeishan large igneous province (China). The Paleoarchean samples from the Barberton Greenstone Belt show μ182W values ranging from –20.4 to +5.6, whereas the Mesoarchean komatiites from the Suomussalmi Greenstone Belt show μ182W values of –2.2 to +7.7. The Permian Emeishan picrites give μ182W values of –7.1 to +3.1. The negative μ182W values observed in the Paleoarchean samples from the Kaapvaal Craton likely result from either early differentiation or core-mantle interaction. Incorporation of this component into the mantle could lower the average μ182W value of the silicate Earth, which would explain the lower μ182W values in some younger granitoids and komatiites relative to most of the Paleoarchean rocks (e.g., Mei et al., 2020; Nakanishi et al., 2023). By combining our results and the published data, the long-term trends in W isotope compositions of mantle-derived rocks provide important insights into the generation, preservation, and destruction of early mantle heterogeneities.

Reference(s)

Mei, QF, Yang, JH, Wang, YF, Wang, H and Peng, P 2020, An improved extraction chromatographic purification of tungsten from a silicate matrix for high precision isotopic measurements using MC-ICPMS: Journal of Analytical Atomic Spectrometry, v. 33, p. 569–577.

Nakanishi, N, Puchtel, IS, Walker, RJ and Nabelek, PI 2023, Dissipation of Tungsten-182 Anomalies in the Archean Upper Mantle: Evidence from the Black Hills, South Dakota, USA: Chemical Geology, v. 617, p. 121255.