Crystallization temperatures of vetreny belt komatiitic basalts, Karelia, based on partition of alumina between olivine and chromite

The Archean-Proterozoic transition in Earth's history is marked by significant changes in mantle dynamics and temperature regimes. A notable consequence is the disappearance of Al-depleted komatiites in the late Archean and the nearly complete absence of true komatiites since the Proterozoic. In this study, we present the investigation of the 2.41 Ga komatiitic basalts of the Vetreny Belt, dating back to the Archean-Proterozoic boundary. These rocks provide unique data on the composition of olivine and chromite, as well as on the crystallization temperatures based on Al-in-olivine geothermometry for Vetreny Belt komatiitic basalts. The temperatures of the earliest stages of crystallization were approximately 1240±25°C, indicating the presence of water in the melt and aligning with measured water contents of 0.4±0.2 wt. % H2O in the melt inclusions. However, during crystallization, the komatiitic basalt melt underwent degassing, resulting in mass crystallization and a temperature rise of approximately 20°C due to latent heat release. The degassing of water from the melt suggests crystallization in the surface conditions.