Sean Yaehne
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B.Sc. (Honours) Thesis
Apatite (U-Th-Sm)/He Thermochronology of the Eastern Arctic Rim: Evolution of the North-Central Baffin Island Rifted Margin
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Along the eastern margins of Labrador and Baffin, Devon, and Ellesmere Islands an extensive highland surface (1300-2000m) divides a narrow, coastal lowland from a series of upland plateau and lowland surfaces that decline in elevation as well as relief to the west. This extensive linear feature is known as the Eastern Arctic Rim and its geomorphologic similarity to other high elevation passive margins suggests that it formed as a result of rifting of Greenland from the North American Craton. This study presents (U-Th-Sm)/He thermochronologic data from north-central Baffin Island to supplement already existing geologic, geophysical and geomorphic interpretation in order to evaluated the evolution of the passive margin since late Cretaceous rift flank uplift altered the islands topographic character.
Interpretations from two sampling transects are presented from the north-central Baffin region, (i) a vertical transect within the Davis Highlands, and (ii) an isolated elevation horizontal transect oriented SW-NE perpendicular to the rifted margin.
On the horizontal transect, a systematic trend is observed with the youngest He ages occurring in a narrow region adjacent to the Baffin Bay margin (~200 Ma), oldest ages in the high elevation Davis Highlands and Baffin Uplands (300 - 350 Ma), and moderately young ages occurring in the west near the Foxe Basin (~250 Ma). This pattern of He ages indicates that margin has been evolving in a manner closely resembling the pinned divide model as described by Gallagher et al., (1998). There is also some evidence that the rift scarp is retreating, following Gallagher et al.'s (1998) other end member model, but down wearing of the elevated margin appears to be the dominant exhumation force. This evidence of the pinned divide model supports the notion that the Baffin Island crustal block has been tilted westwards and that the uplifted margin formed as a result of rift flank uplift.
From the vertical transect a late Paleozoic period of accelerated cooling is observed, but uplift that effected the margin during the late Cretaceous is buried well below sea level. This indicates that the region has been undergoing significantly low exhumation rates, and therefore the exact timing and cause of flank uplift can not be determined.
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Pages: 100
Supervisor: Rebecca A. Jamieson