Deformed sedimentary basins as records of orogenesis

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Orogens (mountain belts) are major features of the Earth, known be formed when buoyant continental lithosphere interacts with convergent plate boundaries. However, explaining their diversity in terms of plate scenarios is a major challenge. The Appalachian-Caledonide orogen formed during Pangea amalgamation. It has an unparalleled stratigraphic, geochronologic, and geophysical database. Previous work has tended to assume that it formed by orthogonal plate convergence, and that stratigraphic units and structures were laterally continuous. Nonetheless, modern plate tectonics tells us that convergence is typically oblique, and that colliding terranes have irregular shapes. The objective of the proposed research will be to explain the substantial along-strike variations in this typical ancient orogen in terms of contrasts and lateral discontinuities in obliquely converging plates. The proposed program will train highly qualified personnel from undergraduate to doctoral level, using field mapping, interpretation of remotely sensed and seismic reflection data, detrital zircon provenance, analogue deformation modelling, and tectonic restoration. Our previous work showed that salt tectonics is under-recognized in the late Paleozoic record of the northern Appalachians; salt movement was triggered by underlying strike-slip faults. A basin-wide tectonic model will allow us to restore the late Paleozoic motion, as a prerequisite to understanding earlier tectonics, and will lead to better understanding of how strike-slip faults interact with salt deposits elsewhere. The earlier history of the orogen involved Ordovician to Devonian accretion of multiple Gondwana-derived terranes to the margin of Laurentia. These accretion events include the Salinic, Acadian and Neo-Acadian orogenies, and led to major, but localized, crustal thickening. We will use detrital zircon U/Pb and Lu/Hf analyses from sandstone deposited during this interval to distinguish between tectonic models for these events. Much of the earliest (Taconic) deformation took place on the Laurentian margin, and is interpreted to record continent-arc collision. However, Laurentian units also high in the Caledonide thrust stack in Baltica have been interpreted as derived from Greenland, but their stratigraphic record has no equivalents there; transport along the orogen must have occurred. We will trace the history and movement of components of the Laurentian margin within the orogen, using modern margins as analogues (e.g. the N Australian margin), and attempt to explain how subduction was initiated following breakup of the earlier supercontinent Rodinia. The proposed research will lead to an actualistic model for the development of the Appalachian Caledonide system incorporating new data and older neglected data sets to fully account for lateral variations in terrane geometry and motion. It will impact the plate-tectonic causes of orogenesis and the search for resources in orogens generally.