Detrital zircon geochronological characteristics of Ruyang and Luoyu Group from western Henan Province and its geological significance

Abstract

Meso-Neoproterozoic sequences are developed in "Yushan Rift Trough" in the southern margin of North China Craton, and Ruyang Group and Luoyu Group are distributed in Mianchi-Qushan stratigraphic unit. The ages of formations have been controversial. In this paper, a systematic detrital zircon geochronology study was carried out from Ruyang and Luoyu Group of Meso-Neoproterozoic sequences, combining with stratigraphic development and rock assemblage, which provides a basis for the establishment of a Meso-Neoproterozoic stratigraphic framework on the southern margin of the North China Craton. The average age of young zircons in the lower part of Yunmenshan Formation is 1723.6 Ma. Considering other geochronology datas from tuff intercalation of Luoyu Formation(1611±8 Ma, 1640±16 Ma, 1638±9 Ma, 1634±10 Ma), the deposition time limit of the Ruyang-Luoyu group was limited to 1720~1600 Ma. The 207Pb/206Pb ages from the samples collected from Yunmengshan Formation, Baicaoping Formation and Cuizhuang Formation were between 2657~1739 Ma, 2712~1780 Ma and 2654~1819 Ma respectively, indicating that the sedimentary materials of the three formations were mainly derived from Paleoproterozoic geological bodies and some Neoarchean geological bodies. The Neoarchean-Paleoproterozoic Taihua Complex, the Neoarchean Dengfeng Group, the Paleoproterozoic Songshan Group and granitic rocks developed in Lushan area can all provide material sources for the Meso-Neoproterozoic sedimentary rocks. The age peaks of ~2.7 Ga, ~2.5 Ga, 2.1~2.0 Ga and 1.85~1.8 Ga from the Ruyang-Luoyu detrital zircons in Western Henan, correspond to important geological events, such as crustal growth, cratonization, rifting and orogenesis in the early Precambrian of the North China Craton, respectively. More and more datas show that the North China Craton had strong magmatism during the period of 2.2~2.0 Ga and the magmatism of ~2.1 Ga in western Henan area has been gradually identified.