Abstract: The CL images and trace element (Th/U>0.4) of clastic zircons from Lower Carboniferous Baishan Formation in Alxa Right Banner indicate that most of them were derived from magma. The age of zircons varies from 412Ma to 498Ma，concentrated on 443~446Ma，the weighted average age is (454.6±8.3)Ma(n=28)，MSWD=3.5, and the degree of confidence is 95%, corresponding probably to that of magmatic arc generated in Middle Tianshan Mountain during the northward subduction and attenuation of Southern Tianshan Ocean on the western lateral of the study area from Ordovician to Early Devonian. These data reveal that Engeerwusu fault is likely to be an Eopaleozoic suture zone belonging to Kazakhstan plate and Huabei plate. The provenance of Baishan Formation is a Caledonian tectonic magmatite zone.