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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Zircon growth and recycling during the assembly of large, composite arc plutons
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Zircon growth and recycling during the assembly of large, composite arc plutons

机译：大型复合弧形聚光体组装过程中锆石的生长和回收

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Concordant U-Pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth. Advances in zircon TIMS analysis and geochronological studies by SIMS on zircon from young volcanic rocks, along with evolving views of the evolution of magmatic systems, makes it necessary to revaluate this interpretation. Assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton. Distinctions must be made between true inherited zircon, xenocrystic zircon derived from host rocks during magma ascent and/or emplacement, and multi-stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons. These complications are exemplified by recent high-precision U-Pb zircon age dating from the Cretaceous Tuolumne and Mt. Stuart batholiths, which clearly show that the timeframe of pluton assembly was long ( ＞ 5 Ma for Mt. Stuart and ＞ 8 Ma for Tuolumne). Zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon (several 10~5 yr up to 2 × 10~6 yr), and assignment of statistically valid rock solidification ages is not possible from these data. Low Zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent. Recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages, and is compatible with progressive growth of a large, long-lived, crystal mush body. Because eruption of magma requires low to moderate crystal fraction and high temperatures (relative to stored crystal mushes), zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions.
机译：传统上一直将一致的U-Pb锆石日期解释为对Pluton的结晶年龄进行约会，因为直到最近，分析不确定性通常都已经足够大到足以涵盖Pluton增长的预期持续时间。 SIMS对来自年轻火山岩的锆石进行锆石TIMS分析和地质年代学研究的进展，以及对岩浆系统演化的不断发展的看法，使得有必要重新评估这种解释。基于锆石测年的独特岩体结晶年龄的分配由于锆石在多个侵入事件中生存的倾向而变得复杂，而这些侵入事件最终形成大型岩体。必须区分真正的继承锆石，在岩浆上升和/或就位时从宿主岩中衍生的异晶锆石，以及在凝固形成大型p体的岩浆储层注蜡和减弱过程中锆石的多阶段生长。这些并发症可以通过最近的白垩纪Tuolumne和Mt的高精度U-Pb锆石年龄来举例说明。斯图尔特岩心清楚地表明，岩钉组装的时限很长（斯图尔特山＞ 5 Ma，图奥勒姆＞ 8 Ma）。来自两个岩基的样品中的锆石晶体对锆石都表现出相当一致的年龄分布（几个10〜5年，直至2×10〜6年），并且从这些数据中无法确定统计有效的岩石凝固年龄。每个基岩岩石中的Zr较低表明，当放置和继承的锆石很少或不存在时，岩浆最初在锆石中强烈不饱和。连续岩浆注入过程中锆石前体的再循环是一致的锆石年龄适度年龄分散的主要原因，并且与大型，长寿命的晶体糊状体的逐步生长兼容。由于岩浆的喷发需要低到中等的晶体分数和高温（相对于储存的水晶糊状菌），因此锆石晶体更可能在大爆发前的热力复原过程中被根除。

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