Cumulate processes in granitic magma systems are thought by some to be negligible and by others to be common and widespread. Because most granitic rocks lack obvious evidence of accumulation, such as modal layering, other means of identifying cumulate rocks and estimating proportions of melt lost must be developed. The approach presented here utilizes major and trace element compositions of hornblende to estimate melt compositions necessary for zircon saturation. It then compares these estimates with bulk-rock compositions to estimate proportions of extracted melt. Data from three arc-related magmatic systems were used (English Peak pluton, Wooley Creek batholith, and Tuolumne Intrusive Complex). In all three systems, magmatic hornblende displays core-to-rim decreases in Zr, Hf, and Zr/Hf. This zoning indicates that zircon must have fractionated during crystallization of hornblende, at temperatures greater than 800 °C. This T estimate is in agreement with Ti-in-zircon thermometry, which yields a maximum T estimate of 855 °C. On the basis of this evidence, concentrations of Zr in melts from which hornblende and zircon crystallized were calculated by (1) applying saturation equations to bulk-rock compositions, (2) applying saturation equations to calculated melt compositions, and (3) using hornblende/melt partition coefficients for Zr. The results indicate that melt was lost during crystallization of the granitic magmas, conservatively at least as much as 40 %. These results are in agreement with published estimates of melt loss from other plutonic systems and suggest that bulk-rock compositions of many granitic rocks reflect crystal accumulation and are therefore inappropriate for use in thermodynamic calculations and in direct comparison of potentially consanguineous volcanic and plutonic suites.

中文翻译：

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大多数花岗石都是堆积的：从角闪石成分和锆石饱和度中扣除

有人认为花岗岩岩浆系统中的堆积过程可以忽略不计，而另一些人则认为它们是普遍且普遍的。由于大多数花岗岩岩石缺乏明显的聚集证据，例如模态分层，因此必须开发其他方法来识别堆积岩石并估算熔体损失的比例。本文介绍的方法利用角闪石的主要和微量元素组成来估算锆石饱和所需的熔体组成。然后，将这些估计值与块岩成分进行比较，以估计提取熔体的比例。使用了来自三个与弧有关的岩浆系统的数据（英吉利峰顶岩体，伍利溪岩基和吐鲁姆侵入复合体）。在所有这三个系统中，岩浆角闪石的中心到边缘显示Zr，Hf和Zr / Hf减小。该分区表明，在角闪石的结晶过程中，温度高于800°C时，锆石必须已经分馏。这个T的估算值与锆石中Ti的测温法一致，后者可产生最大T估计温度855°C。根据这一证据，可以通过以下方法计算出角闪石和锆石从中结晶的熔体中的Zr浓度：（1）对块状岩石成分应用饱和度方程；（2）对计算出的熔体成分应用饱和度方程；（3）使用角闪石/熔化Zr的分配系数。结果表明，熔岩在花岗岩岩浆结晶过程中损失了，保守地至少损失了40％。这些结果与已公布的其他深成系统的熔体损失估计值一致，表明许多花岗岩岩石的块状岩石成分反映了晶体的积累，因此不适合用于热力学计算以及直接比较潜在的近火山岩和深成岩组合。