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

地温计自我一致性评估：迈向更准确的结晶岩浆温度-时间路径的一步

• 批准号: 221141776
• 负责人: Dr. John Hora, Ph.D.
• 金额: --
• 依托单位: Česká geologická služba
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2013-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/221141776?language=en
• 关键词: Evaluation; self; consistency; among; geothermometers

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.

火成岩岩石学的主要目标之一是描述岩浆在喷发前所经历的一系列条件：压力-温度-时间路径。实现这一目标的两种最常见的途径是：(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，或者(2)解释晶体中的分带。目前已有几种基于相间化学成分平衡交换的地温计用于硅质岩浆中。然而，在大多数情况下，它们的校准性能仅通过与自然样品中的一种或两种其他温度计进行比较来验证，并且不存在对整个温度计套件总体自一致性的可靠测量。依赖于分析单相（或晶体生长区域）的温度计提供了一条前进的道路，因为可以从晶体核心到边缘读取一系列温度，但最近这些校准也受到了质疑，各种现有的校准公式需要根据尽可能多的基准进行严格测试。该项目将比较单个自然样品中的大量温度计，目的是评估可用温度计之间的自一致性。如果这些变量的值不是先验的（通常是自然样本的情况），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作为识别异种晶体的一种手段。另一方面，如果平衡可以独立验证（例如，通过微量元素划分），则不一致可能指出可以改进基础温度计校准以获得更一致结果的方法。地温计之间的自一致性将使封闭温度序列作为粗略的T-t路径得到更可靠的解释。更高分辨率的T-t路径需要更精细的空间分辨率，这样就可以测量单个生长区域的温度和年龄。我们的目标是通过有限范围的离子探针工作来评估这一想法的可行性，如果成功，将为后续工作奠定基础。

项目成果

An Excel-based tool for evaluating and visualizing geothermobarometry data

• DOI: 10.1016/j.cageo.2013.02.008
• 发表时间: 2012-12
• 期刊: Comput. Geosci.
• 作者: J. Hora;A. Kronz;Stefan Möller-McNett;G. Wörner