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Crystal-rich volcanic rocks are important for understanding the evolution of large silicic magma systems. However, the magmatic evolution and rejuvenation processes that form the eruptible crystal-rich magma remain controversial. In this study, we conducted petrological, whole-rock major and trace element geochemical and zircon U–Pb and Hf–O isotopic analyses on the Banshan crystal-rich tuff from the large Cretaceous volcanic belt of southeast China. Systematic SIMS and LA-ICP-MS zircon U–Pb geochronology indicate that the Banshan tuff was formed at ∼114–112 Ma. Their zircon Hf isotopic compositions [ε Hf (t) = −10.9 − 4.2; T DMC = 2.18–1.68 Ga] indicate that the magma of Banshan tuff was derived from a combination of mantle-derived melts and partial melting of the Paleoproterozoic crust of southeast China. In addition, they have low zircon O isotopic compositions (δ18O VSMOW = 4.39–5.36‰) reflecting that the assimilation of wall-rocks which underwent high-temperature hydrothermally exchange with meteoric waters. Extremely Mn-rich garnets in the Banshan tuff (MnO = 30.48–35.82 wt%) suggest that the magma once reached a high degree of crystallization which was nearing consolidation. The subsequent mush rejuvenation caused by magma recharge is evidenced by partly resorbed alkali feldspar, quartz and garnet, as well as the CL-bright rims of zircon. Crystal-rich volcanic rocks are widely distributed in the lower sequences of Cretaceous volcanic strata from southeast China, but rarely developed in the upper sequences. We suggest this reflects that the magmas of lower sequences have higher volatile contents and were formed in a subduction tectonic setting. • The Banshan tuff has Mn-rich garnets crystallized from highly differentiated magma; • Magma of the Banshan tuff reached a high degree of crystallization (> 90%). • Rejuvenation of silicic mush triggered the eruption of crystal-rich magma; • Crystal-rich tuff magmas are volatile-rich and formed in a subduction setting. [ABSTRACT FROM AUTHOR]

• Plagioclases from the porphyritic quartz syenite show relatively high (87Sr/86Sr) i. • Plagioclases from the mafic microgranular enclave show low and variable (87Sr/86Sr) i. • Magma recharge is revealed by inter-grain variation of Sr isotope in plagioclase. • Whole-rock Sr isotope is assemblage of plagioclase with different (87Sr/86Sr) i. In situ Sr-isotope of plagioclase can be used to elucidate the details of magmatic processes. Here we report in situ Sr isotopic compositions of plagioclase from the intra-caldera porphyritic quartz syenite and mafic microgranular enclave of the Yandangshan caldera, SE China. Plagioclase phenocrysts from porphyritic quartz syenite show consistent initial 87Sr/86Sr ratios (0.7088–0.7091). Plagioclases in groundmass of mafic microgranular enclave have low initial 87Sr/86Sr ratios (0.7080–0.7081). In contrast, the plagioclase phenocrysts of mafic microgranular enclave show relatively variable initial 87Sr/86Sr ratios of 0.7081–0.7088, which exhibit distinct inter-grain variation with high values similar to the plagioclase phenocrysts in porphyritic quartz syenite, and low values similar to the plagioclase in groundmass. However, the initial 87Sr/86Sr ratios of individual plagioclases from phenocrysts and groundmass show insignificant intra-grain variation. Furthermore, initial 87Sr/86Sr ratios (0.7080–0.7088) of plagioclase from phenocrysts and groundmass of mafic microgranular enclave are within and lower than the whole-rock initial 87Sr/86Sr ratios (0.7082–0.7088), while the values of plagioclase phenocrysts from the porphyritic quartz syenite are within and higher than the whole-rock initial 87Sr/86Sr ratios (0.7086–0.7089). Therefore, we propose that the inter-grain Sr isotope variation of plagioclase is related to magma recharge events, which induce chemical and physical exchanges between the recharge magma and the host magma and the remobilization of crystal mush in magma reservoir. Furthermore, our study shows that whole-rock Sr isotopic compositions could not represent the end-members and they may be a result of the assemblage of rock-forming minerals such as plagioclase with different initial Sr isotopic ratios. [ABSTRACT FROM AUTHOR]

The Cretaceous Yunshan caldera complex in SE China consists of an unusual coexisting assemblage of peraluminous and peralkaline rhyolites and a resurgent intra-caldera porphyritic quartz monzonite. In this study, we use zircon trace element data to study the compositional differences of zircons from cogenetic magmas and to track the evolution of the entire magmatic system. Our results indicate that the zircons from the peraluminous and peralkaline rhyolites formed from highly evolved compositions with high Hf concentrations and low Ti contents, and low Th/U and Zr/Hf ratios, which are distinct from those of the intrusive porphyritic quartz monzonite. Zircons from the peraluminous and peralkaline rhyolites display overlapping Zr/Hf and Hf, but the zircons from the peralkaline rhyolites have extremely low Eu/Eu* ratios (<0.1) and Ti contents (2.26–13.3 ppm). The lack of overlapping zircon trace element compositions between the volcanic and intrusive caldera units is interpreted to represent crystal–melt segregation processes. In addition, zircon grains from the porphyritic quartz monzonite and a few zircon grains from the peraluminous rhyolite display distinctly bright rims and whole grains in cathodoluminescence imaging, which have high Ti, Zr/Hf, and Eu/Eu*, and are similar to those of zircons from the mafic microgranular enclave within the porphyritic quartz monzonite. We interpret these signatures to reflect crystallization from a relatively hot and less evolved magma indicating a magma chamber recharge event. We further developed a model in which the magmas of the peraluminous and peralkaline rhyolites were successively extracted from a primitive crystal mush by crystal–melt segregation with a rejuvenation of the crystal mush after the extraction of the peraluminous rhyolitic melt, leaving behind residual mushes solidified as porphyritic quartz monzonite. Our study shows that trace element analyses of zircons can effectively be used to pinpoint multiple crystal–melt segregation and melt extraction events as well as magma recharge processes in silicic magmatic systems. • Volcanic-plutonic link was revealed by zircon trace elements from caldera complex. • Peralkaline rhyolite extracted from rejuvenated mush after peraluminous rhyolite extraction. • Contrasting compositions of volcanic and plutonic zircons imply crystal–melt segregation. • Multistage zircon crystallization reflects magma recharge processes. [ABSTRACT FROM AUTHOR]