Zircon geochemistry of different intrusive phases of Weiya pluton, implications for magma genesis

1INTRODUCTION Ithasbeenshownthatpetrogenesisofthe granitescannotbefullyexplainedsolelybypetro graphicandgeochemicalstudies.Thisisbecausethegranitesobservedinthefieldanddisplayedby laboratoryanalysisonlyrepresentaparticularstate towardsequilibriumandtheirpresentmineralogyandchemistryartnothingbuttheultimateprod uctsofmagmaevolution.Inaddition,lithological lyvaryinggranitescanoccuratthesametectonic setting,andmineralogicallyandgeochemicallysimilargranitescanbeproducedindiverseenviron ments[1…

Zircon geochemistry of different intrusive phases of Weiya pluton: implications for magma genesis

The characteristics of hosted magmas and their petrogenesis based on electron microprobe determination of trace element contents in zircons were discussed. Trace element geochemistry of zircons indicates that zircons in both gabbro and quartz syenite have two-generations. Zircons of the first generations are crystallized in the magma chamber, whereas those of the second generations are formed in supercooling environment. The former is richer in Zr, but poorer in U, Th, Hf and Y. Quartz diorite porphyrite contains zircons that can be distinguished into the early and late generations. Compared to the late generation, the early generation is richer in Zr but poorer in U, Th, Hf and Y. No conspicuous disruption of zircon evolution has been found in both biotite monzogranite and fine-grained granite. However, the content of zircon in fine-grained granite is higher in U, Th and Y and lower in Zr relative to biotite monzogranite without significant contrast in mass fraction ratio of ZrO2 to HfO2 ratio. Such differences in zircon geochemistry of various intrusive phases and the occurrence of the two zircon generations within a single intrusive phase suggest that these phases of magmas are generated from diverse sources during post-collisional continental extension. These magmas ascend rapidly and cool quickly in a short interval.