GENESIS OF GIANT PROMONTORIES DURING STAGED CONTINENTAL BREAKUP AND IMPLICATIONS FOR EARLY PALEOZOIC LAURENTIA AND ITS SURROUNDING OROGENS
Giant promontories might have formed during the breakup of the supercontinents Rodinia and Nuna but have not been widely recognized. Properties of the modern examples suggest some identifying criteria. They are cored by continental crust that was created or last reworked during the previous collisional cycle. The early histories of the two flanks of a promontory will have different ages and kinematics because separate continents or microcontinents drift away in different directions at different times. The shape of Laurentia and gaps and age jumps along its Paleozoic margins together suggest that promontories dating from breakup of Rodinia may have existed in NE Greenland (potentially displaced to the North Slope of Arctic Alaska), Rockall, Alabama, the Mojave, and the Yukon.
During ocean closure (typically, arc-passive margin collision), a promontory may be exposed to earlier and more intense tectonism than elsewhere along the margin. Unique events are also possible (e.g., south Florida's Paleogene collision with Cuba). Giant promontories are unlikely to have deep lithospheric keels and may be prone to being dislodged and rotated during collision. Thus, what starts as a promontory may end up as a microcontinent in an orogen. Such an origin should be evaluated for microcontinental fragments with passive margin successions in the circum-Laurentian orogenic belts (e.g., Farewell, Cassiar, and Arctic Alaska).