Abstract: Abstract：Blueschists and eclogites are newly recognized in the Hongliuquan area, North Altyn Tagh. These blueschists and eclogites, together with metapelites, calcareous schists and quartz schists, form part of a coherent high-pressure (HP)/low-temperature (LT) metamorphic terrane, which occurs as a tectonic slab in faulted contact with ophiolitic mélanges. P-T estimates show that the peak pressure-temperature metamorphic conditions for the eclogites were 2.0-2.3 GPa and 430-540℃. Phengite from an eclogite sample and paragonite from a blueschist sample were selected for Ar-Ar dating. Phengite from eclogites yields an Ar-Ar plateau age of （512±3）Ma and an isochron age of （513±5）Ma, and paragonite from blueschists gives an Ar-Ar plateau age of （491±3）Ma and an isochron age of （497±10）Ma. These new age data suggest that the North Altyn Tagh HP/LT metamorphic belt probably formed earlier than the North Qilian HP/LT metamorphic belt and imply the existence of diachronism of subduction of the Early Paleozoic oceanic crust beneath the North Altyn Tagh-North Qilian.