Grant: Discovery Grants Program - Individual

Pangea, the most recognizable of Earth Science icons, is the focus of my research. Wegener depicted Pangea as having formed in response to the Carboniferous continental collision of Gondwana in the south with Laurussia in the north giving rise to the Appalachian (in America) - Variscan (in Europe) Orogen. How one interprets the Appalachian - Variscan Orogen is dependent upon the nature of significant map-view bends that characterize both mountain belts. Are these map-view bends 'primary' paleogeographic features (promontories and recesses), or are they secondary 'oroclines' - formerly linear orogens that have been subsequently buckled about vertical axes of rotation? Most models assume the bends are primary structures, and imply that the final collision was preceded by an accretionary period during which 'peri-Gondwanan' continental ribbons (Avalonia; Meguma; South Portuguese Zone) that rifted from the north margin of Gondwana, opening the Rheic Ocean, collided with and accreted to the southern margin of Laurussia. Furthermore, Primary models imply that: 1 - peri-Gondwanan terranes are restricted to a belt bound by the Rheic suture to the south and the Laurussian autochthon to the north; 2 - multiple sutures characterize the southern margin of Laurussia, where they separate the peri-Gondwanan terranes, whereas a single Rheic suture bounds the north margin of the intact Gondwana passive margin; 3 - crustal thickening and orogenesis resulted from entry of the Gondwana passive margin into a subduction zone dipping beneath Laurussia; and 4 - post-collisional deformation of Pangea is explicable in terms of a within-plate, intra-continental tectonic setting. Support for an alternative model comes from our recent research of the Variscan Orogen in Iberia. Paleomagnetic, structural and stratigraphic studies demonstrate that the orogen is characterized by two coupled secondary oroclines that formed between 305 and 295 Ma, and which define a continental scale S-fold. Palinspastic restoration of the oroclines yields a 2300 km long previously linear NNE-striking orogen, and indicate that 1100 km of shortening at translation rates in excess of 10 cm/a was required to produce the oroclines. In our new model of the orogen, in which oroclinal buckling explains the map-view geometry of the orogen: 1 - peri-Gondwanan terranes (South Portuguese zone) lie east of the Rheic suture; 2 - Instead of being bound by a single Rheic suture, the Gondwana passive margin sequence forms a continental ribbon bound to the east by the Rheic suture, and to the west by a separate suture represented by ophiolite in NW Iberia; 3 - Variscan orogenesis is a product of subduction of the Gondwanan ribbon continent to the west beneath an oceanic arc, and not beneath Laurussia; and 4 - so-called post-collisional intra-Pangean orocline formation, which involved 1100 km of translation at rates of >10 cm/a, requires the involvement of subduction and hence the presence of oceanic lithosphere within the heart of Pangea well into the Permian. A program of geological, paleomagnetic, geochronological and geochemical studies focused along select transects across the Variscan orogen will test these contrasting models of Pangea construction. Expected outcomes include an improved understanding of Earth's paleogeography; better constraints on the relationship between Earth System evolution, including extinction events, and the supercontinent cycle; and an augmentation of outreach opportunities including public and school presentations.