 Volcanic activity between 1,890 and 1,864 million years ago produced calc-alkaline andesite-rhyolite magmas and rare shoshonite and trachyandesite magmas while the 1,904‑million-year-old arc volcanism occurred in one or more separate volcanic arcs that were possibly characterized by rapid subduction of thin oceanic crust and large back-arc basins.In contrast, the younger 1,890‑million-year-old volcanics indicate evidence of crustal thickening.This was due to long-term growth of the volcanic arcs by continuous volcanic activity and tectonic thickening associated with arc collisions and successive arc deformation.