10 NORTH AMERICA/Precambrian Continental Nucleus Figure Field photos of representative elements of the Precambrian geology of North America (A) Earth’s oldest intact rocks, the Acasta gneisses, along the western edge of the Slave Craton Ca 4.03 Ga gabbros and tonalitic gneisses cut by 3.6 Ga isoclinally folded granite sheets and younger mafic dykes (B) Ca 2.8 Ga fuchsitic quartzites overlying ancient basement gneisses at the base of the Neoarchaean Yellowknife Supergroup, Slave craton (C) Ca 2710 Ma variolitic pillow basalts of Fe tholeiitic composition, a typical component of Archaean greenstone belts; Yellowknife greenstone belt, Slave Craton (D) Multiply deformed, ca 2660 Ma metaturbidites