Abstract:

The Great Xing’an Range, located within the east part of the Central Asian orogenic belt (CAOB), is composed of E'erguna, Xing’an and Songnen blocks, from north to south. The weakly metamorphosed rock series of the Wolegen Group are mainly distributed in the northern Xing’an block, and were previously regarded as the Neoproterozoic-Early Cambrian strata, in spite of rare reliable geological and geochronological evidence. In this paper, we report the LA-ICP-MS zircon U-Pb ages of the Dawangzi Formation in Wolegen Group. The Dawangzi Formation consists of two lithologic units: the upper unit characterized by low-grade metamorphic volcanic rocks and the lower composed of low-grade metamorphic sedimentary rocks. The zircon dating results show that the metavolcanic rock of the upper unit was formed in the Early Silurian period, its age is  (430.7±4.1) Ma. The meta-sedimentary rock of the lower unit was formed not earlier than the Early Ordovician period as attested by the peak age of (480.1±2.9) Ma of the youngest population of zircons. The existing data show that the low-grade metamorphic rocks of the Wolegen Group are a stratum combination, which formed during the Cambrian to the Early Silurian instead of Neoproterozoic-Early Cambrian period. The zircon geochronology in the rock from the Dawangzi Formation shows that the tectonic emplacement of the Xinlin ophiolites were not older than the Early Ordovician period. The Ordovician clastic sedimentary rocks in Xinlin and Xinglong area were coeval with the Ordovician Duobaoshan volcanic arc volcanism, which indicates that there was an arc-basin system in the Northern Great Xing’an Range during the Early Ordovician period.

Key words: northern Great Xing’an Range, Xinlin area, Wolegen Group, zircon U-Pb dating, volcanic rocks