Typomorphism of the {211}-type zircon

A natural {211}-type zircon has been first discovered in the Pingtan gabbro in the Fujian Province, which is a new type of morphology reported inmagmatic zircons. Investigation of morphology and trace-element chemistry shows two distinct growth stages, Stage 1 and Stage 2. The {211}-type zircon is the earliest crystallized phase of Stage 1 zircon. The low Hf contents and extreme depletion in U, Th and Y indicate that Stage 1 zircon was approximately in equilibration with melt during the crystallization, so that they are regarded as crystallized phase in deeper magmatic chamber. The Zr-saturated gabbroic magma is demonstrated to be derived from mantle magmas by differentiation. The magma differentiation and zircon crystallization at the lower crust level indicate the existence of underplating of mantle magma beneath this area, which results in strong magmatic activities in the late Mesozoic.