U–Pb zircon age, geochemical and isotopic characteristics of the Miaoya syenite and carbonatite complex, central China

Abstract

The Miaoya syenite and carbonatite complex is located in the southern margin of the South Qinling belt, central China. LA‐ICP‐MS zircon U–Pb dating reveals that the syenite and carbonatite have crystallization ages of 445.2 ± 2.6 Ma (MSWD = 0.66) and 434.3 ± 3.2 Ma (MSWD = 1.08), respectively. Both syenite and carbonatite display low I Sr values (0.7004 to 0.7053) and depleted εNd (t) values of +1.1 to +5.5, with one‐stage Nd model ages of 0.65 to 0.94 Ga. Their zircon εHf (t) values are also similarly positive (+3.1 to +8.9), and one‐stage Hf model ages range from 0.71 to 0.92 Ga. Whole‐rock geochemistry suggests that the syenite belongs to the shoshonitic series and both syenite and carbonatite show identical REE and trace element patterns. The coeval intrusive ages, similar geochemical and Sr–Nd–Hf isotopic compositions suggest that the Miaoya carbonatite and associated syenite are genetically related to each other. We consider that the carbonatite could be a final product by protracted fractionation of a CO 2 ‐rich alkaline melt. The depleted εNd (t) and zircon εHf (t) isotopes also indicate that the associated syenite and carbonatite could be originated from a mantle‐derived magma. The sources are likely composed of dominated HIMU mantle and minor EMI mantle. We propose that the Silurian Miaoya Complex was formed in the extensional rifting setting, associated with the mantle upwelling. Copyright © 2016 John Wiley & Sons, Ltd.