Evaluation of self-consistency among geothermometers: a step toward more accurate temperature-time paths of crystallizing magmas

火成岩岩石学的主要目标之一是描述导致喷发的岩浆所经历的一系列条件：压力-温度-时间路径。实现这一目标的两条最常见的途径是：(1)解释具有不同闭合温度的几个相的信息，从而记录不同时间点的条件，或(2)解释晶体中的分带。用于硅质岩浆的地温计有几种，它们是基于相之间化学成分的平衡交换。然而，在大多数情况下，它们的校准性能是通过与自然样品中只有一到两个其他温度计进行比较来验证的，而且整个温度计组合没有可靠的自我一致性衡量标准。依赖于分析单相(或晶体中的生长区)的温度计提供了一条前进的道路，因为温度序列可以从晶体的核心到边缘读取，但最近这些温度的校准也受到了质疑，现有的各种校准公式需要与尽可能多的基准进行严格的测试。该项目将比较单个自然样本中的大量温度计，目的是评估现有温度计之间的自我一致性。如果这些变量的值不是先验已知的(就像自然样本通常的情况一样)，那么拥有比密集变量更多的方程是很重要的。从系综模型中识别异常值可以用作识别捕虏晶的一种手段。另一方面，如果可以独立地验证平衡(例如，通过微量元素分配)，不一致可能指向可以改进基础温度计校准的方法，以得到更一致的结果。地温计之间的自我一致性将允许更稳健地将封闭温度序列解释为粗略的T-T路径。更高分辨率的T-T路径需要更精细的空间分辨率，这样就可以测量各个生长带的温度和年龄。我们的目标是通过有限范围的离子探测器工作来评估这一想法的可行性，如果成功，这将为后续工作奠定基础。

One of the main goals of igneous petrology is to describe the series of conditions experienced by a magma leading up to eruption: a pressure-temperature-time path. The two most common routes to this goal are: (1) to interpret information from several phases that have a variety of closure temperatures, and therefore record conditions at different points in time, or (2) to interpret zoning in crystals. Several geothermometers based on equilibrium exchange of chemical components among phases exist for use in silicic magmas. However, performance of their calibrations are, in most cases, verified by comparison to only one or two other thermometers in natural samples, and no reliable measure of self-consistency exists for the entire suite of thermometers in aggregate. Thermometers that rely on analysis of a single phase (or growth zone in a crystal) offer a way forward, in that a sequence of temperatures can be read from core to rim of a crystal, but recently the calibrations of these, too, have been questioned and the various extant formulations of calibrations need to be rigorously tested against as many benchmarks as possible.This project shall compare a large number of thermometers in a single natural sample, with the goal of evaluating self-consistency among available thermometers. Having more equations than intensive variables is important if the values of those variables are not known a priori (as is often the case with natural samples). Identification of outliers from the ensemble model can be used as a means of identifying xenocrysts. If on the other hand, equilibrium can be independently verified (e.g. though trace element partitioning), discordance may point to ways in which the underlying thermometer calibrations can be improved to give more consistent results.Self-consistency among geothermometers will allow more robust interpretation of a sequence of closure temperatures as a rough T-t path. A higher-resolution T-t path requires finer spatial resolution, such that both temperatures and ages of individual growth zones can be measured. We aim to evaluate the feasibility of this idea via limited-scope ion probe work that, if successful, is intended to form the basis for subsequent work.