James G. Brophy
Professor of Geological Sciences
- Ph.D., 1985, Johns Hopkins University
- M.Sc., 1980, Colorado School of Mines
- B.A., 1977, Amherst College
My primary research interest centers around the chemical and physical processes involved in magmatic differentiation. My work utilizes a wide range of techniques and approaches including geologic field mapping, petrologic and geochemical analysis (major and minor element geochemistry, electron micro-probe) and fluid dynamic modeling. Over the years I have had students conduct research in several areas including the Aleutian Islands, the Cascade Mountains of western Oregon and northern California, the Basin and Range province of the western U.S., and the mid-ocean ridge East Pacific Rise. These studies, largely funded by the National Science Foundation, have considered such diverse topics as the role of subducted crust in the high pressure formation of island arc basalt, the relative roles lower crustal melting, magma mixing and fractional crystallization in the formation of calc-alkaline andesitic magma, the growth and temporal evolution of low-pressure magma chambers beneath subduction-related volcanoes and, finally, the physical mechanisms of low-pressure fractional crystallization in both mid-ocean ridge and subduction zone settings. Most recently, my work has centered around: (1) the role of vapor (H2O) exsolution on the dynamics of magma ascent, crystallization and differentiation of magma; and (2) geochemical modeling of Rare-Earth Element (REE)-SiO2 systematics as a potential means of discriminating between a fractional crystallization and crustal (amphibolite) melting origin for intra-oceanic silicic magmas.
A second area of interest is one-atmosphere experimental petrology. My laboratory has several high-temperature, controlled-atmosphere gas-mixing furnaces that are available for use. Published experimental studies have involved the determination of liquid-lines-of-descent in mid-ocean ridge basalts from the East Pacific Rise; and the solubility of Cu in S-free and S-rich basaltic magmas. Current studies center around the role of crystallization rate on major and minor element partitioning between co-existing clino- and ortho-pyroxene with the ultimate goal of developing a “geospeedometer” to assess crystallization rates in natural magmas.
At the undergraduate level I teach several course for both majors and non-majors including Physical Geology (G111), Earthquakes and Volcanoes (G141), Geochemistry (G406) and Advanced Petrology (G418) . At the graduate level I teach several courses including Volcanology, Advanced Igneous Petrology and Magmatic and Hydrothermal Ore Deposits.
Graduate Student Projects
Stewart, Michael A. (M.Sc., 1992) Petrogenesis of high alumina flood basalts, Steens Mountain, Oregon.
Webster, John Robert (Ph.D., 1992) Petrology of Quaternary volcanics of the Broken Top and Diamond Peak areas, central and south-central Oregon High Cascades: evidence for varied magmatic processes from two contrasting volcanic centers.
Dreher, Scott Travis (M.Sc., 1996) The origin of composition gaps at South Sister Volcano, high Cascades, central Oregon: implications for crystallization processes beneath active calc-alkaline volcanoes.
Whittington, Carla M.(M.Sc., 1996) The petrogenesis of the basalts of Round Head Volcano, Kanaga Island, Aleutians.
Mukherjee, Shibashis (M.Sc., 2007) One-atmosphere investigation of the role of cooling rate on major element partitioning between orthopyroxene and clinopyroxene in andesitic magmas.
Xiaofei Pu (M.S. 2012) Geochemical and petrologic evaluation of lower island arc crust partial melting in the Yakuno ophiolite, Japan
Christian Medina (PhD 2013) Experimental investigation of fluid-rock interaction in the feldspathic Mt. Simon sandstone: Implications for CO2 sequestration in deep-seated sandstone reservoir rocks.
Brophy, JG, and Dreher, TS, 2000. The origin of composition gaps at South Sister volcano, central Oregon: Implications for fractional crystallization processes beneath active calc-alkaline volcanoes. Jour Volcanol Geotherm Res. 102, 287-307.
Ripley, EM, Brophy, JG and Li, C. 2002. Copper solubility in a basaltic melt and sulfide liquid/silicate melt partition coefficients of Cu and Fe. Geochim Cosmochim Acta 66, 2791-2800.
Stewart M, Klein EM, Karson JG, Brophy JG. 2003. Geochemical relationships between dikes and lavas at the Hess Deep Rift: Implications for magma eruptability. J. Geophys. Res. 108, 2184.
Jicha, B.R., Singer, S., Brophy, JG, Fournell, J.H., Johnson, C.M., Beard, B.L., Lapen, T.J. and Mahlen, N.J. (2004) Variable impact of the subducted slab on Aleutian Island arc magma sources: Evidence from Sr,Nd, Pb and Hf isotopes and trace element abundances. Journal of Petrology 45, 1845-1875.
Brophy JG (2008) A study of rare earth element (REE) – SiO2 variations in felsic liquids generated by basalt fractionation and amphibolite melting: a potential test for discriminating between the two different processes. Contrib Mineral Petrol. 156, 337-357.
Brophy JG (2009) Decompression and H2O exsolution driven crystallization and fractionation: development of a new model for low pressure fractional crystallization in calc-alkaline magmatic systems. Contrib. Mineral. Petrol. 157, 797-833.
Brophy JG (2009) La-SiO2 and Yb-SiO2 systematics in mid-ocean ridge (MOR) magmas: implications for the origin of plagiogranite. Contrib. Mineral. Petrol. 158, 99-111.
Sarkar A, Brophy JG, Ripley EM, Li C, Kamo S (2009) Geochemical and isotopic studies of the Lady of the Lake Intrusion: Constraints on the genetic relation between Cretaceous mafic and silicic magmatism in southwestern Montana. Lithos 113, 555-569.
Bowen BB, Ochoa R, Wilkens ND, Brophy JG, Lovell TR, Fischietto N, Medina C and Rupp J (2011) Depositional and Diagenetic Variability Within the Cambrian Mount Simon Sandstone: Implications for Carbon Dioxide Sequestration. Environmental Geosciences 18, 69-89.
Brophy JG, Ota T, Kunihiro T, Tsujimori T, Nakamura E (2011) In situ ion-microprobe determination of trace element partition coefficients for hornblende, plagioclase, orthopyroxene and apatite in equilibrium with natural rhyolitic glass, Little Glass Mountain Rhyolite, California. American Mineralogist 96, 1838-1850.
Brophy JG, Pu X (2012) Rare Earth Element–SiO2 systematics of mid-ocean ridge plagiogranites and host gabbros from the Fournier oceanic fragment, New Brunswick, Canada: a field evaluation of some model predictions. Contrib. Mineral. Petrol. 164, 191-204.
At the departmental level I am in charge of the rock preparation lab and am a member of the undergraduate committee. At the national level I am a regular reviewer of national and international journals, and a grant reviewer for both the Earth Science and Ocean Science divisions of NSF. At the international level I am a panel member for the Science Foundation of Ireland (SFI) Earth Sciences program.