Work performed

The establishing of new microanalytical platform in ISTerre (Figure 2) we consider as one of the major achievements in the first two years of project.
Using this new equipment, we developed a number of new in-situ analytical methods to analyze elemental and isotopic compositions of melt inclusions and host minerals. This allowed us to discover the most depleted in radiogenic 87Sr melt from Earth in a subset of melt inclusions in olivine from 3.3 billion years old mantle-derived melts (komatiites from Barberton Mountain land, South Africa). These melt inclusions correspond to a middle Hadean age (4.2 billion years) mantle source with compositional evidence of significant continental crust production. We performed two highly successful expeditions to remote areas of South Africa and Vietnam to collect samples of komatiites of different ages. A new model has been developed for Ni-Mg-partitioning between olivine and rich in alkalis melt based on new one-atmosphere experiments. We have experimented with annealing of devitrified melt inclusions in zircon.

The temperature, pressure and duration of heating varied in 11 different experiments (900 - 1200 C, 0.1 MPa - 0.5 GPa, 2-24 hr). Zircons were selected from previously studied suites that vary in age from 4.4 Ga to 20 ka, including Hadean samples from the Jack Hills, W. Australia and Barberton, S. Africa. Selected glass inclusions were analyzed by laser-Raman to determine the water content of glass and radiation1 damage in zircon; electron microprobe to determine the chemical composition of glass; and SIMS to determine oxygen isotope ratios of glass and host zircon, the water content of the glass, and age and trace elements in host zircons. We developed new protocols for the analysis of water and of key trace elements such as Nb, Sc and Ta by SIMS. We reported U–Pb/Hf/O data for zircons from Archean Saglek Block, North Atlantic craton,
suggesting that a depleted mantle domain existed in the early Archean and crustal reworking in the Archean.
We develop numerical techniques and run global models of Earth’s evolution spanning its entire age. Our current key finding is that the likely dynamic regime in the Hadean and Eo-Archean times was oscillatory, with interchanging of long-lasted subduction-dominated regimes and shorter non-subduction regimes, rather than previously suggested continuous non-subduction stagnant-lid or squishy-lid regimes.

Updated on 15 March 2023