Chemistry of Hf-rich zircons from the Laoshan I- and A-type granites, Eastern China

Abstract

Abstract Zircon commonly occurs as one of important accessory HFSE-bearing minerals in A-type granite. A detailed electron microprobe study was carried out on zircon from the Laoshan complex, Eastern China, which is composed of I- and A-type granites. Zircon from the I-type rocks is relatively poor in trace elements (HfO 2 <2 wt.%, UO 2 , ThO 2 and Y 2 O 3 <1 wt.%), but that from the A-type rocks is richer in Hf, U, Th and Y. Hafnian zircon with a HfO 2 content of up to 12.37 wt.% was found in the arfvedsonite granite, which is considered the most evolved facies in the A-type suite. Enrichment in Hf is generally observed at the rims of zircon crystals relative to the cores. The Hf enrichment in zircon, and the association of exotic REE - and HFSE-bearing minerals are linked to hydrothermal activity, suggesting that during the last stage of crystallization of the A-type magma, fluids enriched in REE , HFSE, F − , CO 3 2− and PO 4 3− were released.