Harry W. Green II, an American Geophysical Union (AGU) Fellow and distinguished professor at the University of California, Riverside, passed away on 22 September 2017. He was 77.
Harry was a giant in high-temperature, high-pressure mineralogy and petrology, publishing over 150 papers, many with high impact. He had unparalleled vision, energy, and enthusiasm and considerable personal charm. His contributions were as broad as they were deep. He relished tackling key problems from innovative perspectives and did so with a prodigious ability to connect wide-ranging evidence, be it intriguing papers or curious outcrops.
Early Life and Work
Harry grew up in Colorado and earned his B.A. (with honors), M.S., and Ph.D. (with distinction in 1968) from the University of California, Los Angeles. In his doctoral work, he studied deformation and annealing of fine-grained quartz with David T. Griggs and John M. Christie and made the fascinating observation that coesite formed outside of its stability field in highly strained quartz.
Harry then took a postdoctoral fellowship in the Division of Metallurgy and Materials Science, Case Western Reserve University (with S. V. Radcliffe), where he was among the first researchers to investigate experimentally deformed rocks with transmission electron microscopy (TEM). No other scientist used this powerful tool more effectively to investigate the sources and conditions under which mantle rocks ascend to Earth’s surface. Using naturally deformed peridotites in xenoliths from the mantle, Harry focused on deformation processes that control the strength of the upper mantle.
He demonstrated that microstructures around small fluid inclusions were consistent with the notion that fluid inclusions were exhumed from depth with the host xenoliths, corroborating the subsolidus nature of the asthenosphere and revealing the impact of fluids on deformation of mantle rocks. Beginning in the mid-1970s Harry also teamed with U.S. Geological Survey scientist Dale Jackson and Adolphe Nicolas at the University of Nantes to sample and study mantle xenoliths from Hawaii and the classic Alpine peridotites of southern Europe. Thus, as Harry began his illustrious career as a professor in the University of California (UC) system (first at UC Davis and then, starting in 1993, at UC Riverside), he had already defined the broad scientific themes that became the hallmarks of his career: the interaction between deformation and phase transformations, the importance of microscopic features, and a lifelong interest in the rheology of the mantle.
Phase Transformations and Earthquakes
Building upon his early interest in the interaction of phase transformations and deformation, Harry and his graduate student Pamela Burnley discovered unequivocal evidence of faulting associated with the kinetic onset of transformation from olivine-structured magnesium germanate (Mg2GeO4) to its spinel phase. The team found that faulting was accompanied by a unique microstructure, which consisted of lenticular bodies of ultrafine-grained spinel and spinel-filled shear zones. Realizing the similarity between the stress state around the spinel lenses and that around stylolites, Harry dubbed the spinel lenses “anticracks,” a term coined earlier for stylolites.
Kinetically hindered transformation of metastable olivine is expected in cold subducting slabs; thus, transformational faulting provides an elegant mechanism for triggering deep-focus earthquakes. Harry and Pamela’s landmark discovery appeared in a series of publications in the early 1990s and spawned a flurry of seismological and experimental studies to test this mechanism further. Harry also advanced this work by using acoustic emissions to “hear” the seismic events both in germanate analogues and in samples of true olivine compositions at higher pressures. Additionally, he worked on other phase transformations and dehydration reactions in eclogite and serpentinite to explain the occurrence of intermediate-depth earthquakes.
The observation that fault surfaces induced by phase transformation are filled by ultrafine-grained spinel led him to pursue a unified mechanism of earthquake ruptures. One of his latest papers showed convincing evidence that the propagation of all earthquake ruptures is likely a consequence of grain boundary sliding of a very thin and exceedingly weak “gouge” of nanocrystalline particles that form at the onset of sudden sliding. Such a rheological behavior is insensitive to pressure, a trait that makes it quite counterintuitive to our notions about brittle ruptures. Nonetheless, this new finding is entirely consistent with the odd, near-orthogonal pattern of rupture propagation during the great 2012 earthquake sequence in the Indian Ocean.
Subduction Zones and Ultrahigh-Pressure Metamorphism
Harry was always convinced that careful studies of microstructures and mineralogy could reveal the rich geologic history of xenoliths and mantle rocks. In 1995, together with Larissa Dobrzhinetskaya, Harry used exsolved mineral precipitates in olivine crystals of garnet peridotite to demonstrate that the Alpe Arami massif had been exhumed from a great depth of 300 kilometers, more than double any previous estimates of deep exhumation. This study prompted researchers around the world to look for microstructural evidence of deep exhumation in peridotites, eclogites, and metasedimentary rocks. The result is wide recognition of the very deep origin of such rocks, with major implications for tectonic processes during subduction of lithospheric plates and continental collision.
Harry and his colleagues played a key role in ultrahigh-pressure metamorphism by demonstrating how an integration of field studies, carefully planned high-pressure experiments in state-of-the-art apparatuses, and microanalytical techniques on both natural and synthetic samples can constrain depths of rock exhumation. Their arsenal of techniques included nanoscale secondary ion mass spectrometry, scanning electron microscopy, TEM, focused ion beam, Raman spectroscopy, and Fourier transform infrared spectroscopy. Harry also collaborated with colleagues on the formation of nanodiamond from supercritical fluids. This collaboration also identified the first nitrides in mantle rocks, including the first boron-bearing mineral from the mantle, qingsongite, and found the first evidence of the coesite-stishovite transformation in metamorphic rocks from orogenic belts and in ophiolitic metasedimentary rocks. In doing so, Harry helped establish the new field of “nanomineralogy,” demonstrating that micro- and nanominerals often retain unique petrological information, similar to the way in which trace elements carry geochemical information not available from major elements alone.
Service and Community
Harry was a generous collaborator across disciplines. He was also an effective mentor to numerous young scientists, students, and postdocs, who all remember him as fair and kind, with profound integrity and a wry sense of humor.
His service to the scientific community was extraordinary, including serving as chairman of the Executive Committee of the Consortium for Materials Properties Research in Earth Sciences and as president of the Tectonophysics section of AGU and therefore as a member of the AGU Council. At UC Riverside, he served as the vice chancellor for research, in which role he impressively streamlined the process of proposal submission, and as chair of the Department of Earth Sciences several times.
A fellow of the Mineralogical Society of America (MSA), the American Association for the Advancement of Science, and AGU, Harry delivered AGU’s fourth Birch Lecture in 1995. He received the Bowen Award from AGU’s Volcanology, Geochemistry, and Petrology section, MSA’s Roebling Medal, and, shortly after his passing, the European Geosciences Union’s Louis Néel Medal.
Harry is survived by his wife and many children and grandchildren, as well as numerous students, postdocs, and colleagues, who will all miss him tremendously.
—Pamela C. Burnley (email: [email protected]), University of Nevada, Las Vegas; Wang-Ping Chen, Faculty of Geophysics and Geomatics, China University of Geosciences, Wuhan; also at Department of Geology, University of Illinois at Urbana-Champaign, Urbana; Larissa F. Dobrzhinetskaya, Department of Earth Sciences, University of California, Riverside; Zhen-Min Jin, School of Earth Sciences, China University of Geosciences, Wuhan; Haemyeong Jung, School of Earth and Environmental Sciences, Seoul National University, South Korea; Robert Liebermann, Department of Geosciences and Mineral Physics Institute, Stony Brook University, N.Y.; Manuela Martins-Green, Department of Molecular, Cell and Systems Biology, University of California, Riverside; Alexandre Schubnel, Laboratoire de Géologie, Ecole Normale Supérieure/Centre National de la Recherche Scientifique, PSL Research University, Paris; Yanbin Wang, Center for Advanced Radiation Sources, University of Chicago, Ill.; and Junfeng Zhang, School of Earth Sciences, China University of Geosciences, Wuhan