Is the Trans-Hudson Orogen a Large, Hot Orogen? Insights From Orogenesis and Cooling on Hall Peninsula, Baffin Island

English Abstract:

The Trans-Hudson Orogen extends with a northeasterly strike for over 4600 km from the United States to northern Canada, and has an across-strike width of about 400-800 km. It has a long-lived accretionary history, beginning with amalgamation of crustal blocks in the upper Churchill plate during ca. 1.92 to 1.84 Ga, and ending with its terminal collision with the lower Superior plate at ca. 1.83-1.80 Ga. The orogen likely possessed a high heat flow, as it includes voluminous charnockitic batholiths and extensive granulite terranes. As such, in many ways it conforms to the definition of a large, hot orogen, comparable to the modern-day Himalayan orogen. Granulite-facies metasedimentary rocks on Hall Peninsula, southeast Baffin Island can be used to further explore this notion since they contain significant partial melt and host charnockitic plutons. The dominant deformation mechanism in the granulite facies terrane is km-scale east-vergent folding. Monazite U-Pb ages coupled with mica Ar-Ar geochronology on Hall Peninsula indicates cooling rates of ~1-2°C/Ma from peak metamorphism in the mid-crust at ca. 1.85-1.83 Ga to cooling through muscovite closure temperatures at ca. 1.67-1.64 Ga. This slow cooling rate and the lack of extensional structures suggest that this segment of the Trans-Hudson Orogen did not experience orogenic collapse despite a flat Moho and average crustal thickness of 43 km. In fact, much of the Trans-Hudson Orogen exhibits slow cooling rates and is missing many of the hallmarks of collapse, such as core complexes or significant detachments. The absence of these features sets the Trans-Hudson Orogen apart from other large, hot orogens such as the Grenville, Variscan and Himalayan orogens.