Jason B. Saleeby
Professor of Geology, Emeritus
CONTINENTAL MARGIN TECTONICS
Professor Jason Saleeby has worked on a broad spectrum of geological problems aimed primarily at developing a better understanding of the tectonics of the earth's mountain belts and, in particular, ocean basin continental margin interactions and crustal-formation processes along western North America. Saleeby utilizes structural and stratigraphic field techniques, isotope geochronology and geochemistry, and petrologic investigations in his regional studies. He collaborates with a number of researchers from the U.S. Geological Survey, as well as U.S. and international academic researchers, in studies which cover a wide geographic area. In addition, Saleeby performs detailed strategic studies on his own and supervises a wide range of graduate student thesis projects.
Professor Saleeby has recently completed a detailed structural and geochronologic study of the Duke Island ultramafic intrusion and its wallrocks in southeast Alaska. Using integrated U/Pb zircon and Sm/Nd bulk rock and mineral studies, he has shown that the intrusion was emplaced at ~110 million years ago. The structural studies show that the intrusion was emplaced during a regional extension event which occurred over a broad region of southeast Alaska and which resulted in the development of a large sedimentary basin. Shortly following the emplacement of the intrusion, the region underwent a major thrust faulting event which led to the closure of the basin, regional uplift and en masse transport of the intrusive complex along a basement-rooted thrust fault. Regional work by Saleeby and Charles Rubin (Caltech Ph.D., 1991) show that this thrusting event occurred between 105 and 95 million years ago and that it affected a nearly 1200 km long segment of the Pacific Coast orogen.
A significant portion of Saleeby's career has been devoted to the tectonic and geochronological analysis of southwest North American ophiolite belts. Through these efforts and in conjunction with a number of collaborators, an integrated model of ophiolite generation and emplacement has emerged. The main proposition of the model states that the unique architecture of the southwest U.S. sialic edge and its outer armor of composite ophiolite belts are intimately related. The sialic edge has undergone multiple phases of transform truncation, while the adjacent ophiolite belts record multiple phases of transform tectonic and petrogenetic phenomena. This unique history is shown to have extended back into Paleozoic time. Subduction tectonics and arc magmatism have been interspersed in time and space, and hybridized with transform tectonics. As part of this ongoing research, Caltech graduate student Doug Yule has performed a detailed structural and geochronologic study of the northern part of the Josephine ophiolite in southern Oregon. Doug has delineated rafted fragments of older lithosphere within the Josephine massif that were attenuated, broken apart, rafted into and engulfed in juvenile oceanic lithosphere as the Josephine ophiolite formed by transform-controlled oblique rifting in an interarc basin system during the Late Jurassic.
Regional structural, petrogenetic, and geochronological studies of the southern half of the Sierra Nevada batholith by Saleeby and a group of Caltech graduate students and professional colleagues have revealed interesting results which will help elucidate Phanerozoic sialic crustal genesis. These studies show that for composite batholithic rocks of mid-Cretaceous age (~100 million years ago), structural continuity exists between shallow volcanic levels in the central part of the range and the deep granulitic levels at the southern end of the range. The granulitic levels display a wide array of deep batholithic tectonic and petrogenetic phenomena. The structural framework established for the southern half of the batholith offers a superb laboratory for the exploration of igneous and metamorphic petrogenetic phenomena and material transport patterns within one of the world's great Phanerozoic batholithic belts.
Professor Saleeby is also a leader in a joint U.S. Academy of Sciences-Russian Academy of Sciences comparative study program between the Greater Caucasus Mountain Range of southern Russia and the Sierra Nevada Mountains of California. Saleeby has hosted a Soviet team of scientists studying comparable geological phenomena in the Sierra Nevada region. He has initiated field studies in the Greater Caucasus Mountain Range and will conduct geochronological and isotopic studies aimed at resolving the late Precambrian-Paleozoic evolution of the continental basement and ophiolitic fragments of the range, Mesozoic Tethys margin rifting of the basement, Alpine thrusting and uplift, and Neogene plutonism and ignimbrite activity.
Professor Saleeby has also been a leader in the Decade of North American Geology (DNAG) effort to bring together and synthesize the most up to date body of data and ideas concerning the geological evolution of North America. Major contributions published in 1993 include a synthesis of Triassic and Jurassic tectonics of the conterminous U.S. Cordillera, and a separate synthesis of the tectonic and petrogenetic settings of all major ophiolite complexes for the conterminous U.S. Cordillera.