Mark S. Ghiorso

Mark S. Ghiorso (born October 21, 1954) is an American geochemist who resides in Seattle, Washington. He is best known for creating MELTS, a software tool for thermodynamic modeling of phase equilibria in magmatic systems.

Education Ghiorso earned an AB, MS, and PhD from the University of California, Berkeley. He chose Berkeley for practical reasons: "I went to Berkeley because it was the local school, because tuition was essentially free, and because I was fascinated as a high school student with hot springs, volcanos, and, in particular, the work of Howell Williams and Arthur L. Day." He was promoted to associate professor (a tenured position) three years later and to full professor in 1986. He served as department chair from 1994 to 1999.

In 2003, he was hired by the University of Chicago. Leaving the UW was a difficult decision, as Ghiorso is a great believer in public education. He cited serious concerns about the UW administration as a primary reason for departing.

In 2005 he decided to leave academia and dedicate himself full-time to research. He returned to Seattle and, with his colleague Richard Sack, founded the small non-profit research company OFM Research, where he is vice president and senior research scientist.

Ghiorso has also served as associate editor for the following scientific journals: American Journal of Science (1990–present); American Mineralogist (1990–1993); Geochimica et Cosmochimica Acta (1991–1993); and Contributions to Mineralogy and Petrology (2015–present),

Scientific contributions As an undergraduate, Ghiorso wrote an honors thesis on the hot springs in the Devil's Kitchen area of Lassen Volcanic Park. This work was never published. At or near the surface, the magma cools and crystallizes. Depending on the conditions, it may have time to cool uniformly, or fractional crystallization can occur if parts of the magma are removed after they crystallize.

An early model for fractional crystallization, which explained why certain types of mineral tend to be found together in igneous rocks, was Bowen's reaction series, formulated in 1922. Bowen found that, as magma crystallizes, it separates into two series: a continuous series of minerals that continuously adjusts their composition through interactions with the melt, and a discontinuous series of minerals that remain fixed in composition as they cool. Thus, the type of mineral indicates the temperature at which it was formed.

Until the 1960s, interpretation of the igneous rock record was largely qualitative. Ian Carmichael wanted to determine quantitative information such as the temperature and pressure of the magma when crystals were formed as well as dissolved water and oxygen content. For this, thermodynamic models were needed. Although attempts to apply rigorous thermodynamics to igneous processes go back to at least 1949, they were hindered by a lack of experimental data. Using tools such as a drop calorimeter and wet chemistry, Carmichael and colleagues set out to systematically explore thermodynamic properties of magma at high temperatures. Carmichael hired Richard Sack in 1980, and Sack began extensive experiments that went into a more sophisticated model that was published in 1983, when Ghiorso was at the University of Washington. Ghiorso wrote a program in FORTRAN 77 that he distributed to other researchers.

After the publication of MELTS, Ghiorso continued to improve and extend it with the help of colleagues such as Mark Hirschmann, Paul Asimow, Pete Reiners and Victor Kress. After they identified some fundamental problems with the theory at high pressure, they developed pMELTS, a model for high pressures (1-3 gigapascals (GPa)), and published it in 2001. In 1998, Ghiorso, Hirschmann and Tim Grove established the Library of Experimental Phase Relations (LEPR), an online database for experimental results on solid-melt equilibria. With Guilherme (Guil) Gualda, he modified MELTS to work better with rhyolite, a silicate-rich series of rocks, and released rhyolite-MELTS. With Dmitri Sverjensky of Johns Hopkins University, Ghiorso is leading a Deep Carbon Observatory project to integrate MELTS with the Deep Earth Water Model (DEW) created by Sverjensky. The DEW program models water-rock interactions to depths of 200 km. The movement of carbon between silicate melts and aqueous fluids is still poorly understood. For a paper published in Computers & Geosciences, he received the Best Paper Award from its publisher, the International Association for Mathematical Geosciences. He was elected Fellow of the Mineralogical Society of America in 1993, the Geological Society of America in 1997, and the American Geophysical Union in 1999. The Mineralogical Society of America made him a Distinguished Lecturer for 1996–1997, elected him Councilor for 1997–2001, awarded him the Dana Medal in 2003, and elected him president in 2021. He received the Bunsen Medal from the European Geosciences Union in 2010 and the Norman L. Bowen Award from the VGP Section of the American Geophysical Union in 2014. MELTS, pMELTS, and thermodynamic properties calculators LEPR, a database portal for experimental data on mineral-melt equilibria MagmaSat (Mac) and MagmaSatApp (iPad), software to compute saturation conditions of H2O-CO2 mixed fluids in natural composition silicate melts