Amp-TB2: An Updated Model for Calcic Amphibole Thermobarometry

Filippo Ridolfi

doi:10.3390/min11030324

Abstract

Amphibole (Amp) plays a crucial role in the study of several earth and planetary processes. One of its most common applications is in thermobarometry, especially for volcanic-magmatic systems. However, many thermobarometers require the input of melt composition, which is not always available in volcanic products (e.g., partially crystallized melts or devitrified glasses), or show rather high errors for characterizing the depth of magma chambers. In this work, a new version of amphibole thermobarometry based on the selection of recently published high-quality experimental data is reported. It is valid for Mg-rich calcic amphiboles in magmatic equilibrium with calc-alkaline or alkaline melts across a wide P-T range (up to 2200 MPa and 1130 °C) and presents the advantage of being a single-phase model with relatively low errors (P ±12%, T ±22 °C, logfO2 ±0.3, H2O in the melt ±14%). A user-friendly spreadsheet (Amp-TB2.xlsx) for calculating the physico-chemical parameters from the composition of natural amphiboles is also reported. It gives warnings whenever the input composition is incorrect or diverges from that of the calibration data and includes diagrams for an easy graphical representation of the results.

Highlights

Amphibole (Amp) is one of the most common mafic minerals in the lithosphere, the major component of some types of rocks, and plays a crucial role in the understanding of several planetary, earth, and health issues [1,2,3,4,5,6,7].The word “amphibole” means ambiguous, from the Greek αμφιβoλoς
The composition of Amp can be used as a tracer for volatile concentrations in melts and fluids, but one of its most common applications is in geothermobarometry, especially for volcanic systems, e.g., [9,12,13]
Thermobarometric models based on chemical equilibria among coexisting mineral-mineral or mineral-melt pairs [9,14,15,16,17] are useful tools widely used to estimate the P-T path and chemical evolution during igneous processes, their application is difficult whenever different magmas interact within the crust and erupt to form mixed products [18,19,20]

Summary

Introduction

Amphibole (Amp) is one of the most common mafic minerals in the lithosphere, the major component of some types of rocks (e.g., amphibolite and hornblendite), and plays a crucial role in the understanding of several planetary, earth, and health issues [1,2,3,4,5,6,7].The word “amphibole” means ambiguous, from the Greek αμφιβoλoς An updated version of the single-Amp model of [10], based on recently published high-quality experimental data, is reported together with a user-friendly spreadsheet to calculate crystallizing P, T, f O2 , and H2 Omelt (volatile content in the melt) conditions of Mg-rich calcic amphiboles in equilibrium with calc-alkaline or alkaline melts.

Results

Conclusion