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Abstract Trace elements in igneous zircon crystals are variable within single crystals or amongst populations of crystals and are particularly sensitive to changes in melt composition. In this study, we present zircon trace element data from both volcanic and plutonic rocks of the Yandangshan caldera complex from SEChina. The erupted rhyolitic rocks are interpreted to represent the most differentiated magma, whereas the intruded porphyritic quartz syenites are thought to be representative of the residual crystal mush. The zircon crystals of both lithologies are subdivided into two types based on their internal structures: type A with a distinct oscillatory growth zoning and type B crystals are bright in cathodoluminescence (CL-bright). Type B zircon occurs as rims of type A zircon or as individual grains. Compared to type A, type B zircons commonly show lower Hf, U, Th and Y concentrations and higher Ti and Zr/Hf and Eu/Eu* ratios. The zircon trace element compositions of the volcanic samples generally overlap those of the intracaldera porphyritic quartz syenite and mafic microgranular enclaves that contain both type A and type B zircons. Despite a general overlap, zircon grains from the volcanic rocks show relatively higher Hf contents and Y/Dy ratios, lower Ti contents and Th/U ratios and larger negative Eu anomalies than the plutonic samples. We suggest that the inter- and intragrain compositional variability of zircon crystals can be used to track the evolution of magmatic systems. We show that in our case, the volcanic and plutonic rocks crystallized continuously during the magmatic evolution in a common magma system and that the magmas of these rocks may be linked by fractional crystallization. Furthermore, the type B zircon grains are inferred to have crystalized in relatively hot and less evolved magma indicating a magma recharge event. Consequently, the geochemical variability of igneous zircon crystals can be used to infer on the magmatic evolution of single volcanic system which may also be applicable in other geodynamic environments. Highlights • Two types of zircon occurred in the Yandangshan volcanic and plutonic rocks. • The volcanic-plutonic connection was revealed by zircon trace elements. • The zircon from different rock units crystallized continuously. • Magma recharge processes were recorded in the zircon domains and some grains. • The compositional variability of zircon can be used to track the magmatic evolution. [ABSTRACT FROM AUTHOR]

The association of volcanic and shallow plutonic rocks in caldera may provide important clues to the geochemical evolution of silicic magma systems. The Yandangshan caldera is a typical example of late Mesozoic volcanic–plutonic complex in SE China. It is composed of a series of rhyolitic extrusives and subvolcanic intrusions of porphyritic quartz syenites. In this work, we conducted petrological and geochemical studies, as well as zircon dating, on the coexisting volcanic and plutonic rocks from the Yandangshan caldera. The results of SHRIMP and LA-ICP-MS zircon U–Pb dating revealed that the crystallization of the rhyolitic extrusives and subvolcanic intrusions was contemporaneous within analytical errors and in a short period (104–98 Ma). Geochemically, the volcanic rocks are characterized by high Rb/Sr and Rb/Ba ratios and depletion in Ba, Sr, P, Eu and Ti, while the shallow plutons show high K, Ba, Al, Fe and low Rb/Sr and Rb/Ba ratios with insignificant negative Eu anomalies. The volcanic and plutonic rocks have a similar range of zircon Hf isotopic compositions ( ε Hf ( t ) = − 10.0 to + 1.5) and T DM2 model ages of 2.10–1.23 Ga. They also have comparable whole-rock Sr and Nd isotopic compositions (( 87 Sr/ 86 Sr) i = 0.7084–0.7090; ε Nd ( t ) = − 7.8 to − 6.5) and zircon oxygen isotopic compositions ( δ 18 O mainly = 4.5 to 6.0‰). We argue that the volcanic–plutonic complex of the Yandangshan caldera was formed by reworking of Paleoproterozoic lower crusts in the eastern Cathaysia block, and that the complex could be linked by fractional crystallization and crystal accumulation in a shallow magma chamber. The volcanic rocks represent the highly fractionated end-member, whereas the subvolcanic intrusions of porphyritic quartz syenites could be the residual crystal mushes. This case study could have a general implication for the genetic relationship between volcanic and shallow plutonic rocks in calderas. [ABSTRACT FROM AUTHOR]

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]