Abstract

Zircon samples separated from the gabbro - diabase in Núi Nưa area, Thanh Hóa were dated by LA-ICP-MS U-Pb method, giving the age of 470 Ma, which is deemed as their crystallization age. These gabbro-diabase bodies penetrated the ultramafic rocks of Núi Nưa complex, therefore it can be confirmed that the crystallization age of the ultramafic rocks in the Sông Mã ophiolite zone must be older than 470 Ma (Ordovician). This study is of important significance in delimiting the emplacement age of the ultramafic rocks of Núi Nưa complex in Sông Mã structural zone, one of controversial issues in the last period.