Morphology and geochemistry of zircon: a case study on zircon from the microgranitoid enclaves

There are three types of zircon (i.e. Zircon A, Zircon B and Zircon C) in t he microgranitoid enclaves from the Qingtian granite. Zircon A is of the sm allest I-pr, I-py and I-el values with the largest range of variations; Zir con C is of the largest I-pr, I-py and I-el values with the smallest range of variations; and Zircon B is intermediate among the three types. The micr oprobe analysis of zircon demonstrates that the contents of trace elements (Hf, U, Y, Th) increase progressively with larger and larger variation from Zircon A through Zircon B to Zircon C, These characters suggest that the t hree types of zircon in the enclaves may have formed successively during th e cooling process of enclave magma, corresponding to different sites dong w ith the intrusion of enclave magma. Because of positive correlations of the UO2/HfO2, ratio with I-pr, the ThO2/Y2O3 ratio with I-py, and the UO2/(ThO 2 + Y2O3) ratio with I-el, it is suggested that the variation in zircon typ ology is caused by selective substitution of trace elements on different su rfaces of zircon. On the basis of enclave petrology and zircon typomorphism , it is believed that the enclave magma may be generated from partial melti ng of residual materials in deep regions where the granitic magma has been extracted.