THE CONTRIBUTIONS OF DAVID L. JONES TO CORDILLERAN GEOLOGY: A CANADIAN PERSPECTIVE

David (Davy) L. Jones spent the first 30 years of his geological career with the USGS in Menlo Park, and the last 10 years at UC Berkeley. He started work when Cordilleran tectonic evolution was framed in the context of the geosynclinal cycle, and he was the biostratigrapher in the classic 1964 paper by Bailey, Irwin and Jones on "eugeosynclinal" Franciscan and "miogeosynclinal" Great Valley sequences in California. The paper provided the base for recognition in the later 1960s that these sequences represented respectively an ancient subduction complex and a forearc basin, and placed California in the forefront of the application of plate tectonic concepts to on-land geology. By 1972, evolution of the entire Cordillera had been interpreted within the plate tectonic paradigm. Also in 1972, Davy's colleague Porter Irwin first used the term "terrane" in the Klamath Mountains, and Davy and others suggested that older rocks in southeastern Alaska were a displaced continental fragment. In 1977, Davy had named what is perhaps the best-known Cordilleran terrane - Wrangellia -characterized by its distinctive early Mesozoic stratigraphy and paleomagnetic signature. By 1980, the Cordillera was viewed as a collage of "suspect terranes" accreted to the Laurentian continental margin, and the terrane concept became exported and applied worldwide to analyses of of other orogenic collages. Davy "Henry Ford-ized" the method developed by Emile Pesagno in 1972 for extracting radiolarians from their chert matrices, which resulted in many new ages from previously undateable rocks and in all Cordilleran subduction complexes having wider age spans than previously recognized. This had major tectonic and paleogeographic implications in Canada, where the Cache Creek complex, previously known to contain only late Paleozoic fossils, lays continentward of Alexander, Stikine and Wrangellia terranes, and is now known to be as young as Early Jurassic. In the last part of his career, Davy and Berkeley colleagues suggested that rapid extrusion of Triassic basalt in Wrangellia resulted from an underlying mantle plume. The above summary of Davy's contributions does not do him justice. His energy, enthusiasm and strong opinions at meetings in the 1970s and early '80s made them thought-provoking and exciting, and catalyzed Cordilleran tectonic thinking.