Abstract: Detailed geochemical study shows that the Wanggaxiu gabbro complex from the North Qaidam has characteristics of island arc volcanic, likely formed in a sitting of an island arc. Cathodeluminescence investigations and trace elements analyses of zircons separated from the gabbro reveal that all zircons display relative wide oscillatory zoning, high abundances of REE and HREE, the REE patterns of depletion in LREE, and strong enrichment in HREE are of the features of zircons derived from basic magma. LA-ICP-MS U-Th-Pb isotopic analyses yield a 206Pb/238U weighted average age of 468 Ma±2 Ma, and a maximum concordant age of 522 Ma±9 Ma, implying that the Wanggaxiu gabbro complex was formed during 468~522 Ma. The determination of island arc type of Wanggaxiu gabbro complex, together with the previous studies on the Tanjianshan volcanics, suggesting the existence of Paleozoic oceanic event in the North Qaidam, and the slab subduction start at least from mid-Ordovician. And considering of this point, the age of the continental deep subduction of the North Qaidam should not be earlier than 460 Ma.