Pioneer of quantitative microanalysis and chemical thermodynamics in igneous petrology
Ian Carmichael, larger-than-life petrologist who introduced quantitative microanalysis and chemical thermodynamics into igneous petrology, died in Berkeley, California on 26 August 2011.
Carmichael was born on 29 March 1930 and educated in London. During the final year of secondary school he made an exchange visit to a school in Connecticut and thereafter enrolled himself for one semester in the Colorado School of Mines. This began his lifetime fascination with the rugged terrain of the western USA. He returned to England for National Service and took a short-service commission in the paras. This ended with him severely damaging both knees during landing (apparently on a house – the condition of the house afterwards remains unknown).
Ian did his BA in Cambridge where he came under the influence of C E Tilley. Since Tilley did not, apparently, want him as a PhD student he moved to Imperial College where he began research under supervision of George P L Walker. His thesis (1958) focused on Thingmuli, a Tertiary volcano in eastern Iceland. Ian used his field and petrographic skills to address one of the most contentious issues in Earth science at the time, namely the origin of silicic magma, and whether it could form solely by crystal fractionation of basalt, or whether assimilation of older continental crust was required. The problem went to the very heart of crustal evolution, and his was a classic demonstration of the evolution of basalt to rhyolite.
On completion of his thesis, Ian became a lecturer at Imperial College. He developed his research on the crystallisation paths of feldspars in silicic magmas and became close friends with William S MacKenzie, who was following similar ideas experimentally in Manchester. In 1963, Ian took a six-month leave at the University of Chicago, where one of the first electron microprobes was being demonstrated. He quickly realised that this instrument would revolutionise petrology and therefore asked to extend his leave to collect more data. When his request was refused Ian resigned, finding himself aged 34, with a wife and three young children, in Chicago, in the dead of winter, without a job. Before long he was invited to the University of California, Berkeley to give a lecture and this turned into a tenured position as an Associate Professor.
In 1964, when the study of magmatic rocks was largely descriptive, Ian Carmichael was asking detailed questions about whether the crystals in erupted lavas could be used quantitatively to determine the temperatures, pressures, dissolved water concentrations, and oxidation states of the magmatic liquids from which they crystallised. The answers necessitated, firstly, detailed microanalysis of crystals and matrix and secondly a thermodynamic approach to crystal-melt equilibrium. The latter was hindered by the lack of information on the thermodynamic properties of magmatic liquids under
in situ high-temperature conditions.
Nevertheless, Ian and his students came up with innovative ways of estimating and extrapolating these properties, which gave him some bones to support his thermodynamic approach. Soon thereafter (1971) he discovered a moth-balled calorimeter in the Materials Science department and he and his students began to measure the properties of silicate liquids, including their compressibilities from sound speed measurements, and their heat contents up to 1700°C. One of the best-known fruits of this work is the MELTS computer program of one of Ian’s students, Mark Ghiorso. Despite, however, his emphasis on microanalysis and experiment Ian’s research was always field-orientated and he maintained an active field programme into his 70s.
Ian Carmichael was a wonderfully generous and dedicated mentor. Almost all of his 29 PhD students hold faculty or related positions in US universities and the USGS. When I arrived as a temporary lecturer from Manchester (1973) he took me under his wing, asking “What are you working on at the moment ?”. “I’ve just had a paper accepted”, I replied. “Let me see”. Two hours later he said: “Interesting idea - but you didn’t consider many of the implications. Even though it’s accepted, withdraw it and I’ll pay the costs. You can work on the MS over the next few months while the grad students and I criticise it until it’s
really ready for publication.”
At that time Ian was Department Chairman in Berkeley, a position he held on two separate occasions. He also spent 15 years as Associate Dean and Associate Provost at UC Berkeley, at the same time serving as Editor-in-Chief of Contributions to Mineralogy and Petrology. In 1986 he was invited to review my department at Northwestern University at a time when we feared closure. Once Ian and Karl Turekian (Yale) had reported and browbeaten the Dean, the University reprieved us, delivered a pat-on-the-back and awarded us an extra faculty position.
Ian was a Fellow of the Royal Society. His contributions were also recognised by the Bowen Award (AGU), the Day Medal (GSA,) the Murchison Medal (GSL), the Schlumberger Medal (Min. Soc., GB), and the Roebling Medal (Min. Soc. Am.).
By Bernard Wood