Genesis of zircons with core?rim structure from HP?UHP gneisses of the Dabie Mountains
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摘要: 大别山高压?超高压片麻岩中的锆石在阴极发光(CL)显示核?边结构：韵律环带的岩浆锆石核，较强发光的变质边。本文对核?边结构的锆石进行了包裹体、微区U?Pb年龄和微量元素研究。结果表明变质边由两种不同的机制形成：变质重结晶和变质增生。变质重结晶锆石的U?Pb年龄和稀土总量逐渐降低，稀土配分模式不变。变质增生锆石比变质重结晶锆石具有更低Th/U比值，重稀土严重亏损，Eu负异常不明显，低的Nb、Ta含量。Abstract: Most of zircons in high?pressure and ultrahigh?pressure gneisses from the Dabie Mountains show the core?rim structures in their Cathodoluminescence(CL)images，consisting of inherited magmatic cores with oscillatory zoning and the rims of metamorphic origin with bright CL images. The researches，on the basis of the inclusion minerals determined by using Laser Raman microprobe，U?Pb ages and trace elements analyzed by using LA?ICP?MS suggest that the metamorphic rims of zircons was formed through two different mechanisms：recrystallization and overgrowth. Recrystallization could result in gradually decreasing U?Pb ages and total contents of rare earth elements(REE)，but the REE pattern remains unchanged. Comparing with the recrystallization zircons，the overgrowth zircons have no negative Eu anomaly，lower Th/U ratios and contents of Nb and Ta，more depleted HREE.
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