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 [sic] and Arthur L. Day."
Career In 1980, Ghiorso was hired by the University of Washington (UW) as assistant professor in the department of geological sciences. 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. He also holds affiliate faculty appointments at the University of Washington and Vanderbilt University. 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. During his graduate work he continued to do experimental work related to acid sulfate hot springs until he became interested in attempts by Ian Carmichael to create a model for solutions in silicate liquids that could be used as a geothermometer for igneous rocks.
Background In igneous petrology, geologists attempt to learn more about volcanic systems through the record in igneous rocks. Most magma is generated in the mantle through a process called decompression melting. As material rises and the pressure decreases, solidus declines until part of the mantle can melt. 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.
Thermodynamic models Ghiorso began working with Carmichael on silicate-liquid models in 1978, and in 1980 they published their first geothermometers. 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. Ghiorso and Sack realized, however, that the model needed to become more sophisticated. At first, NSF program managers were skeptical of this computational approach, and Ghiorso had three NSF proposals turned down. Fortunately, he managed to persuade the Digital Equipment Corporation to fund his work. After a decade of publishing thermodynamic data on minerals such as olivine and feldspar, Ghiorso and Sack presented their new model, now called MELTS. Their 1995 publication in Contributions to Mineralogy and Petrology became the journal's most cited paper, with more than 2,100 citations as of early 2017. 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. Asimow and co-authors published phMELTS, a model for mid-ocean ridge basalts that incorporated the effect of water content. 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. Ghiorso is the lead investigator on an NSF collaborative research grant to develop ENKI (Enabling Knowledge Integration), a Web-based model-configuration and testing portal for computational thermodynamics and fluid dynamics. He is the lead principal investigator on the project. 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.
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