New thinking and understanding for the researches on the basement of Ordos Block

Based on the comprehensive petrographic observations for the basement samples from deep drilling cores and their zircon U-Pb geochronological data, Hf isotopes and whole rock Nd isotopes of the granitic gneisses as well as aeromagnetic anomaly and velocity distribution of upper crust, a 2. 2 similar to 2. 0Ga arc-magmatism belt is recognized along the NE trending Datong-Huachi fault which goes with the southern fringe of a gradient belt of aeromagnetic anomaly in the basement of central Ordos Block. This arc-magmatism belt had been experienced 1. 95 similar to 1. 85Ga metamorphism similar to those of central part (Trans-North China Orogen) of North China Craton, leading to a two-fold subdivision of the basement of Ordos Block into the northern and southern parts, rspectively. Of which, the northern part displays an EW trending distribution zone of aeromagnetic anomaly, and contains a basement composed by supracrustal rocks including metapelite and metagraywackes gneisses, schists, marbles and quartzites associated with strong migmatization as well as granitic gneisses. It is a terrane with a Neoarchean basement that underwent multiple phases of 2. 5Ga and 2. 2 similar to 2.0Ga magmatic and 1. 95 similar to 1. 85Ga metamorphic events. The southern part is characterized by a NE trending distribution zone of aeromagnetic anomaly and a basement with the reports of strong modification of the 2. 2 similar to 2.0Ga granitic magmatism and a 1. 95 similar to 1. 85Ga metamorphism, suggesting an old block with a basement composed of Paleo- to Meso-Archean and Neoarchean juvenal crustal materials. Consequently, we proposed that the Datong-Huachi fault is most likely a main boundary separated the basement of the Ordos Block. The northern part likely constructed an activity belt of continental margin formed on the Neoarchean basement together with Konderite belt to the north during Late Paleoproterozoic. While, the southern part is a block with a basement composed of some Paleoto Mesoarchean and Neoarchean crust, most likely representing a main part of Ordos Block basement.

Automated summary

Based on petrographic observations, geochronological data, and isotopic analyses of basement samples, a 2.2-2.0Ga arc-magmatism belt is identified in the Ordos Block. The basement is divided into northern and southern parts, with different geological histories. The Datong-Huachi fault likely separates these two parts, with the northern part forming a continental margin on Neoarchean basement and the southern part representing the main part of the Ordos Block basement.