DensityX: A program for calculating the densities of magmatic liquids up to 1,627 °C and 30 kbar

Kayla Iacovino,Christy B Till

doi:10.30909/vol.02.01.0110

Abstract

Here we present a standalone program, DensityX, to calculate the densities of hydrous silicate melts (1000s of samples in a single model run) given pressures, temperatures, and major oxide compositions in wt.% in the 10-component system SiO2-TiO2-Al2O3-Fe2O3-FeO-MgO-CaO-Na2O-K2O-H2O. We use DensityX to analyze over 3,000 melt inclusions over a wide compositional range to visualize the distribution of natural silicate liquid densities in the Earth’s crust. The program is open-source, written in Python, and can be accessed and run via an online interface through a web browser at https://densityx.herokuapp.com or by downloading and running the code from a github repository. A companion Excel spreadsheet can also be used to run density calculations identical to those in the Python script but only for one sample at a time. In another example application, we demonstrate how DensityX can be used to constrain density-driven convective cycling in the phonolitic lava lake of Erebus volcano, Antarctica.

Highlights

The density of a silicate melt affects a myriad of physical and magmatic processes, including magma mixing [Grove and Baker 1983; Jull and Kelemen 2001], melt migration dynamics [Stolper et al 1981; Hack and Thompson 2011], and crustal storage [Sparks and Huppert 1984; Walker 1989; Chaussard and Amelung 2014]
A significant amount of effort has been put into modeling silicate melt densities, which relies upon determination of thermodynamic parameters such as partial molar volumes of major oxide from experiments conducted at a range of pressure (P ) and temperature (T ) conditions and expressions describing changes in the volume of these components as a function of P and T
Coworkers who produced a series of papers describing the densities of the major components of silicate liquids [Lange and Carmichael 1987], thermodynamic relations needed to calculate silicate melt density at elevated P and T [Lange and Carmichael 1990; Kress

Summary

Introduction

The density of a silicate melt affects a myriad of physical and magmatic processes, including magma mixing [Grove and Baker 1983; Jull and Kelemen 2001], melt migration dynamics [Stolper et al 1981; Hack and Thompson 2011], and crustal storage [Sparks and Huppert 1984; Walker 1989; Chaussard and Amelung 2014]. In the Ghiorso-Kress approach, Fe-bearing systems are speciated into three (rather than two) components: FeO, Fe2O3, and FeO1.3 This new treatment and expanded database resulted in an improved model recovery of density measurements in Fe-bearing systems but requires knowledge of the melt oxygen fugacity. We present a standalone program, called DensityX, to calculate the densities of hydrous silicate melts given pressures, temperatures, and major oxide compositions in wt% in the 10-component system. SiO2 TiO2 Al2O3 Fe2O3 FeO MgO CaO Na2O− K2O H2O, using thermodynamic data for these components from Lange and Carmichael [1987], Lange [1997], Kress and Carmichael [1991], and Ochs III and Lange [1999]

Program DensityX

Description of the program package

Densities of natural silicate liquids

Applications to high-P melts

Conclusions

A Appendix 1