Geological and Geochemistry Characteristics of Volcanics in the Late Paleozoic Maoniushan Formation in Amunike Area of Northern Qaidam Basin

The volcanics in Amunike area of Northern Qaidam Basin distribute in late Paleozoic Maoniushan Formation.It was composed of large numbers of acidic volcanic rocks and a small amount of intermediate volcanic rocks with some thin-bedded sedimentary rocks mezzanine such as dolomite and calcareous argillaceous siltstone. The volcanic facies can be divided into eruptive facies, effusive facies and volcanic sedimentary facies with Columnar Joint characteristics. Results of major elements shows a feature of S-type granites, while the REE and trace elements both illustrate a similarity with island arc volcanic rocks which formed in intraplate setting. The discovery of Lepidodendropsis sp., finding in the sedimentary rocks mezzanine,was one kind of standard fossils for Middle Devonian, and obtaining of zircon ²⁰⁶Pb/²³⁸U isotopic age of (369.2±3.3)Ma、(392.4±3.3)Ma in dacites can define the age of these volcanic rocks are Middle-Late Devonian, that significantly later than the East Kunlun area. We can concluded that magmatic activity and geotectonic evolution between the East Kunlun area and northern margin of Qaidam basin are not synchronized.