Seminar

The Labrador Trough, a sub-province of the Canadian Shield, is a fold and thrust belt composed of three cycles of volcano-sedimentation. The late Palaeoproterozoic, ~1.88 Ga Sokoman Formation, a typical granular iron formation (GIF), is part of the second cycle. In addition to primary and altered magnetite in iron formations, magnetite in volcanic breccia associated with the iron formation is identified for the first time in the stratigraphy. Trace elemental compositions of magnetite in the Sokoman Iron Formation were obtained by LA–ICP-MS. The comparisons of different types of magnetite in the iron formation show distinct provenance discrimination. Rare-earth element geochemistry implies the source of iron derived from high-temperature hydrothermal activities on the seafllor. The Fe isotopic compositions of the iron formation indicates a condition with mixing of equilibrium and kinetic iron isotope fractionation during redox reactions and mineral precipitation.

During the early precipitation of the Sokoman Formation, hydrothermal activities on the seafloor may have been associated with the upwelling magmas. Multiple influxes of materials are generated by exhalative volcanic processes. Mineralizing fluids associated with magmas that formed the Nimish volcanic suites circulated through the sedimentary piles to further enrich the iron formations forming magnetite with variable compositions. The iron formation was deposited in a shallow marine setting under a suboxic environment near the redoxcline.