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 ISr 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 CO2‐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.

Hydrothermal upgrading as an important tool for the REE mineralization in the Miaoya carbonatite-syenite complex, Central China

“…volcanic rocks of the Yaolinghe Group), we speculated that the so-called "syenites" samples in Xu et al (2014) could be xenoliths of the country rocks (particularly that the Miaoya complex contains 2.5 vol% xenoliths). For the carbonatites, Zhu et al (2016) and Ying et al 2017obtained similar zircon ages of ~430 Ma. This age should be reliable as these zircon grains are characterized by low U and high Th/U ratios, similar to zircons crystallized from carbonatitic magmas (Yuan et al, 2008).…”

“…3f). Xu et al (2014) has obtained zircon ages of Ma for the syenites, but such ages were suggested to be unreliable by Zhu et al (2016) and Ying et al (2017) who both obtained a similar zircon age of Ma for the syenites. Considering that an age of 766 Ma is comparable to those of the country rocks (i.e.…”

“…This study confirms that the formation of the Miaoya complex and associated REE mineralization involved two separated stages. Both the syenites and carbonatites formed from partial melting of the upper mantle under a rift setting at ~430 Ma (Xu et al, 2014;Zhu et al, 2016;Su et al, 2019;Zhang et al, 2019a), likely followed by a combined fractionation-immiscibility process ( co-genetic with the coeval orogenic Au-Ag mineralization in the same belt, pervasively metasomatized the early carbonatites and syenites (Fig. 13b).…”

Fingerprinting REE mineralization and hydrothermal remobilization history of the carbonatite-alkaline complexes, Central China: Constraints from in situ elemental and isotopic analyses of phosphate minerals

“…Two carbonatite-alkaline complexes with low-grade REE mineralization, the Miaoya and Shaxiongdong complex, South Qinling Belt of Central China, were selected to evaluate their REE mineralization histories in this study. Both complexes have zircon U-Pb ages of 440-430 Ma, which have been interpreted as intrusive ages (Xu et al 2008;Ying et al 2017;Zhu et al 2017;Chen et al 2018;Su et al 2019). However, previous studies also reported monazite ages of ~230 Ma, which has been interpreted as either an independent REE mineralization (Xu et al 2014) or an REE remobilization event (Ying et al 2017;Zhang et al 2019).…”

The age and geochemistry of the Bardkish syenite, northwest Iran: Syenite formation during Neo‐Tethyan subduction

“…Burmakina & Tsygankov, 2013; Mingram, Trumbull, Littman, & Gerstenberger, 2000; Vernikovsky et al, 2003); and (vii) fractional crystallization (with or without crustal assimilation) of mantle‐derived magmas (e.g. Litvinovsky et al, 2002; Mingram et al, 2000; Riishuus et al, 2005; Zhu et al, 2017). The petrogenesis of syenite remains a subject of considerable controversy, and some models are in direct conflict with the results of experimental studies.…”