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首页> 外文期刊>Contributions to Mineralogy and Petrology >Decoupled crystallization and eruption histories of the rhyolite magmatic system at Tarawera volcano revealed by zircon ages and growth rates
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Decoupled crystallization and eruption histories of the rhyolite magmatic system at Tarawera volcano revealed by zircon ages and growth rates

机译：塔拉威拉火山流纹岩岩浆系统的结晶和喷发史解耦的锆石年龄和增长率揭示

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摘要

We obtained U-Th disequilibrium age data on zircons from each of the four rhyolite eruptions that built Tarawera volcano in the last 22 ka within the Okataina Volcanic Center (OVC), caldera, New Zealand. Secondary ion mass spectrometry analyses on unpolished euhedral crystal faces that lack resorption features show that crystal growth variously terminated from near-eruption age to ~ 100 ka prior to eruption. Age-depth profiling of crystals reveals long periods of continuous (~ 34 ka) and discontinuous growth (~90 ka). Growth hiatuses of up to ~40 ka duration occur, but do not all relate to obvious resorption surfaces. Age differences up to similar magnitude are found on opposing faces of some crystals suggesting episodes of partial exposure to melts. These features are best explained by periodic, complete, or partial, sub-solidus storage and/or inclusion in larger crystal phases, followed by rapid liberation prior to eruption. This is supported by high abundances of U and Th (~ 500 - >2,000 ppm) in some zircons consistent with periods of high crystallinity (>70%) in the magmatic system, based on crystal/melt partitioning.
机译：我们从新西兰破火山口Okataina火山中心（OVC）的最后22 ka内建造塔拉威拉火山的四个流纹岩喷发中的每一个获得了锆石的U-Th不平衡年龄数据。二次离子质谱分析对未抛光的，没有吸收特征的正反面晶体表面显示，晶体生长从近萌芽年龄到萌芽前〜100 ka终止了各种变化。晶体的年龄深度剖析揭示了长时间的连续（〜34 ka）和不连续生长（〜90 ka）。出现了长达约40 ka的生长裂口，但并非都与明显的吸收表面有关。在某些晶体的相对面上发现了年龄差异，幅度相似，表明部分暴露于熔体中。可以通过周期性，完全或部分亚固相线存储和/或包含在较大的结晶相中，然后在喷发前快速释放来最好地解释这些特征。基于晶体/熔体分配，某些锆石中的U和Th含量较高（〜500-> 2,000 ppm），与岩浆系统中的高结晶度时期（> 70％）相符，这证明了这一点。

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