THE GEOLOGICAL CONTRIBUTIONS OF DAVE BISH: NOT JUST IN SOILS BUT ALSO IN CRYSTALLINE ROCKS

Dave Bish’s contributions to earth and planetary science are diverse, far exceeding the scope of this session. Beyond the clay, soil, and nanoscience research for which he is so well known, we were fortunate to collaborate with Dave at Indiana University on studies investigating metamorphic processes. One area involved the quantification of K-feldspar polymorphs and deviations from ideal structural coherency (microstrain peak broadening) via XRD to track fluid-assisted recrystallization associated with low-temperature deformation. Also, at low grade, careful XRD analysis of the slates of Taiwan, with particular attention to the discrimination and characterization of phyllosilicate species, Dave helped deepen our understanding of the ductile Lishan Fault zone, and the metamorphic processes active during ductile deformation. At higher grade, in the polydeformed staurolite schists of New England, subtle variations in XRD patterns allowed for the quantification of relic and recrystallized muscovite populations. These data were critical both in interpreting geochronologic results and in evaluating the role of metamorphic reaction in accommodating deformation. Applying similar methods to some of the most abundant rocks in the crust XRD analyses of cores from the Hess Deep Rift off the East Pacific Rise revealed the events and the extents of hydrothermal alteration in lower oceanic crustal rocks. The integration of these data with whole-rock geochemical and isotopic results allowed the identification of reaction pathways and placed constraints on the extents of metasomatism in these gabbros and troctolites with global implications for H₂O cycling. In all of these studies, XRD and careful application of Rietveld refinements were crucial components in unraveling the role of fluids and mineral recrystallization in crustal metamorphism and deformation. All this would not have been possible without Dave Bish’s expertise and patience—thanks Dave, it was fun.