Zircon SHRIMP U-Pb ages, geochemical characteristics and environmental evolution of the Early Precambrian metamorphic series in the Lushan area, Henan, China

The Early Precambrian in the Lushan area, Henan, is divided into the Neoarchean Dangzehe Formation-complex and TTG series and the Paleoproterozoic Taihua Group-complex including the Tieshanling, Shuidigou and Xuehuagou formation-complexes. The author obtained the youngest detrital zircon SHRIMP U-Pb ages of 2.250-2.310 Ga and a metamorphic zircon age of 1.84±0.07 Ga for graphite-sillimanite gneiss of the Shuidigou Formation-complex, and a magmatic zircon SHRIMP U-Pb age of 2.146±0.02 Ga and a metamorphic zircon age of 1.87±0.01 Ga for garnet-bearing gneissic granite intruded into the Xuehuagou Formation-complex; thus the age of the Taihua Group-complex can be determined to be Paleoproterozoic. The analysis of the geochemical characteristics indicates that: the Dangzehe Formation-complex indicates an island arc environment; the Tieshanling Formation-complex has the characteristics of evolution from the intraplate rift to shallow sea; the Shuidigou Formation-complex was formed in an enclosed shallow sea; and the Xuehuagou Formation-complex has the features of an initial ocean basin. The area experienced a lengthy evolutionary process from the subduction and amalgamation of paleocontinental nuclei in the Neoarchean through the crustal breakup and extension into an initial ocean basin to the amalgamation of terranes and oceanic basin closing to form a craton during the Paleoproterozoic.