SYN-EMPLACEMENT OPHIOLITES AND RELATIONSHIP TO SUPERCONTINENT CYCLE
Seminars
Semester 2
Prof. Peter Cawood obtained undergraduate and PhD degrees from the University of Sydney and has held academic positions in Australia, New Zealand, Canada, and the UK. He is currently ARC Laureate Fellow at Monash University and is an elected Fellow of the Australian Academy of Sciences, the Royal Society of Edinburgh, and the Geochemical Society and European Association of Geochemistry. Peter Cawood's research focuses on the origin of the Earth's continental lithosphere (crust and upper mantle) and the processes of its generation, stabilization and reworking. His major research contributions include: demonstrating that the archive of Earth history is not simply a record of the processes of crustal generation but markedly biased by the supercontinent cycle; innovative studies on the early stages of collisional orogenesis that link ophiolite generation to its emplacement; a model for the deformation and stabilization of accretionary orogens, and temporal relations to collisional orogenesis; the role and timing for initiation of plate tectonics on the early Earth; and the application of microanalytical techniques to unravel the provenance history and paleogeography of sedimentary basins and orogenic belts.
Ophiolites are fragments of oceanic lithosphere now entrained within continents. Some ophiolites, such as the Bay of Islands ophiolite in the Appalachian-Caledonian Orogen and the Semail ophiolite in the Alpine-Himalayan Orogen, are characterized by a metamorphic sole along their structural base. The sole records metamorphism along a subduction zone interface between upper and lower plates with structural imbrication resulting in an inverted metamorphic assemblage of higher grade over lower grade. The sole is juxtaposed with the ophiolite, which forms through extension in the upper plate of the subduction zone, during attempted subduction of, and subsequent emplacement onto, a continental margin. Such ophiolites form in small interior ocean basins during supercontinent breakup with generation and expansion of these oceans compensated by lithospheric compression and initiation of multiple subduction zones. Subduction initiation is induced adjacent to a continental margin, likely along lithospheric discontinuities such as transform systems that formed during continental lithospheric extension and interior ocean basin formation. In such newly formed subduction zones, the subducting plate has limited lateral extent enabling its rapid evolution through trench rollback leading to ophiolite generation in the upper plate. This infant subduction system consumes the narrow tract of oceanic lithosphere adjacent to the continental margin leading to ophiolite obduction through attempted margin underthrusting. The establishment of these secondary subduction systems within small interior ocean basins corresponds temporally with the termination of convergent plate interaction and plate reorganization elsewhere in the global plate network, which is the likely primary driver, triggering a cascading sequence of events, that induces the initiation of these transient secondary systems.