Zircon trace element geochemistry constrains on the silicic volcanic system
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P578.94+1;P588.11

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    Abstract:

    The magmatic system of large silicic volcanic eruptions (with ejected volumes of about 102~104 km3) extends through the crust, comprising complex generation, transport, storage, recharge and eruption processes. Critical aspect for understanding the evolution of silicic volcanic system is to reveal the magmatic processes from melt generation to eruption, such as crystal fractionation, crystal accumulation, crystal-melt segregation, crustal assimilation, magma recharge and mush rejuvenation. Zircon incorporates a variety of trace elements, such as Th, U, Ti, Hf and rare earth elements, and their abundances and variations are particularly sensitive to the composition, temperature, oxidation state, water content of the magma and the co-crystallized phases. Therefore, zircon has the outstanding capacity to record the evolution of silicic magmatic system. In general, as the falling temperature of the melt, the Hf concentration increases and the Ti concentration and Th/U, Eu/Eu* and Zr/Hf ratios typically decreases, which are effective indicators of fractionated magmas. Zircon from porphyry intrusions associated with mineral deposits tends to have high Ce4+/Ce3+ and Eu/Eu* ratios, indicating strong oxidized conditions and high water concentration. Zircon can show characteristics of multistage crystallization with a core-rim structure, including distinctly resorbed core and CL-bright rim. Compared to the zircon core, CL-bright rim commonly shows lower Hf and U and higher Ti and Eu/Eu* ratios, indicating magma recharge event and the rejuvenation of crystal mush. Due to the mobility of smaller zircon relative to the larger crystals, zircon may continuously be mobilized in extracting melts recording a continuous compositional range of magma evolution, but may also remain in the crystal mushes indicating crystal-melt segregation events. Zircon trace element compositions integrated by high-precision zircon U-Pb geochronology can track the evolution of silicic volcanic system as a function of time. Metamictization, sector zoning and exotic mineral inclusions should be considered to screen magmatic trace element signatures and interpret the zircon trace element data. Careful examination of thin sections of rock to find zircon occurring and associated minerals is also important to track the multiple evolution of silicic volcanic system.

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贺振宇,颜丽丽,2021,锆石微量元素地球化学对硅质火山岩浆系统的制约[J].岩石矿物学杂志,40(5):939~951. HE Zhen-yu, YAN Li-li,2021,Zircon trace element geochemistry constrains on the silicic volcanic system[J]. Acta Petrologica et Mineralogica,40(5):939~951.

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History
  • Received:January 17,2021
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  • Online: September 16,2021
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