A discussion on the geological characteristics, formation age and attribution of basic volcanic rocks in Yueyashan area, Inner Mongolia

A NWW-trending basic volcanic rock belt is exposed from east to west in the Yueyashan area. The basic volcanic rock belt is composed of layered basalt, pillow basalt and altered basalt. Previous views concerning the attribution of volcanic rocks are controversial. The volcanic rocks are distributed at the center of Yueyashan ophiolite tectonic melange belt and are spatially closely associated with the ophiolite. Volcanic pillow structure is well developed in this set of volcanic rocks, showing the characteristics of submarine volcanic eruption. Petrochemical and geochemical studies show that this set of volcanic rock has typical normal mid-ocean ridge basalt (NMORB) characteristics. Therefore, the Yueyashan basic volcanic rock belt should belong to the part of the Yueyashan ophiolite suite. The authors obtained isotopic age of about 530Ma for gabbro diorite which invaded this volcanic rock belt and also obtained isotopic ages of about 527Ma to 530Ma for gabbro and plagioclase granite. These age values are equivalent to the age of Early Cambrian, indicatiang that the age of the basic volcanic rocks is Early Cambrian.