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A simple and robust method for calculating temperatures of granitoid magmas

Duan, M. and Niu, Yaoling and Sun, P. and Chen, S. and Kong, J. J. and Li, J. Y. and Zhang, Y. and Hu, Y. and Shao, F. L. (2022) 'A simple and robust method for calculating temperatures of granitoid magmas.', Mineralogy and petrology., 116 (1). pp. 93-103.

Abstract

Calculating the temperatures of magmas from which granitoid rocks cumulate is a key task of studying their petrogenesis, but few geothermometers are satisfactory. Zircon saturation thermometry has been the most widely used because it is conceptually simple and practically convenient, and because it is based on experimental calibrations with significant correlation of the calculated zircon saturation temperature (TZr) with zirconium (Zr) content in the granitic melt (i.e., TZr  ZrMELT). However, application of this thermometry to natural rocks can be misleading, resulting in the calculated TZr having no geological significance. The thermometry requires Zr content and a compound bulk compositional parameter M of the melt as input variables. As the Zr and M information of the melt is not available, users simply use bulk-rock Zr content (ZrBULK-ROCK) and M to calculate TZr. In the experimental calibration, TZr shows no correlation with M, thus the calculated TZr is only a function of ZrMELT. Because granitoid rocks represent cumulates or mixtures of melt with crystals before magma solidification and because significant amount Zr in the bulk-rock sample resides in zircon crystals of varying origin (liquidus, captured or inherited crystals) with unknown modal abundance, the ZrBULK-ROCK does not in any way represent ZrMELT that is unknown. Hence, ZrBULK-ROCK cannot be used to calculate TZr or to estimate magma temperatures. As an alternative, we suggest to use the empirical equation TSiO2/MgO (°C) = 1127.5  (SiO2/MgO)[-0.055] for granitoid studies, not to rely on the exact values of individual samples but focus on the similarities and differences between samples and sample suites for comparison. This simple and robust thermometry is based on experimentally determined phase equilibria with T  MgO and T  1/SiO2.

Item Type:Article
Full text:Publisher-imposed embargo
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1007/s00710-021-00769-5
Publisher statement:Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Date accepted:29 October 2021
Date deposited:11 August 2021
Date of first online publication:22 November 2021
Date first made open access:25 January 2022

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