Plate Tectonics, Precambrian

Abstract

Precambrian (>541 million years, Myr) is divisible into the Hadean Eon (>4.0 billion years, Gyr), Archean Eon (4.0-2.5 Gyr), and the Proterozoic Eon (2.5-0.54 Gyr). The Archean and Proterozoic Eons are further divisible into Eras: Eo-archean (4.0-3.6 Gyr), Paleo-archean (3.6-3.2 Gyr), Mesoarchean (3.2-2.8 Gyr), Neo-archean (2.8-2.5 Gyr), Paleoproterozoic (2.5-1.6 Gyr), Meso-proterozoic (1.6-1.0 Gyr), and Neo-proterozoic (1.0-0.541 Gyr). The Phanerozoic Eon corresponds to <541 Myr. These Era names are also used with no hyphen. Zircon (ZrSiO 4) is a mesosilicate found as an accessory phase in a wide compositional range of igneous, metamorphic, and sedimentary rocks of all ages. Zircon crystallizes in silicate melts and incorporates a wide range of high field strength incompatible elements; most common is Hafnium (Hf) with abundance ranging generally up to 4% by weight. Zircon is used widely in geochronology by the U-Th-Pb method of radiometric dating.