PETROLOGY AND AGE OF ECLOGITES OF THE SOUTHERN BROOKS RANGE, NORTHERN ALASKA

It is widely accepted that Jurassic(?)-Cretaceous convergence between a passive margin and the Angayucham island-arc terrane gave rise to the Brooks Range orogeny in Northern Alaska. The orogenic belt comprises a north-directed fold-thrust belt and two metamorphic belts, including the blueschist/eclogite Schist Belt, one of the largest blueschist belts in the world. Although the Schist Belt largely displays greenschist assemblages with evidence for earlier blueschist metamorphism, two eclogite bodies have been identified and sampled. A structural, petrologic, and geochronologic interpretation of the Schist Belt is critical for understanding the tectonics of the Brooks Range orogeny. However, the age of high-pressure metamorphism in the Schist Belt remains unclear, with estimates ranging from >170 Ma to ca. 130 Ma. This uncertainty has resulted in diverse tectonic models of Brooks Range evolution. To improve our understanding of the high-P metamorphism, we present results of (1) mineralogic/petrologic textural analysis of the two eclogite bodies of the Schist Belt and (2) in-situ LA-ICP-MS U-Pb analyses of zircon, rutile, and titanite in eclogite. Dating will be tied to petrography (e.g., inclusions in garnet, rutile rimmed by titanite) in order to date prograde and peak P metamorphism as well as exhumation.

The data collected in this study will provide important new timing constraints on the age of high-P metamorphism and subsequent exhumation. These data will be used to test models for exhumation of the high-P rocks, better understand the timescales of the Brooks Range orogeny, and the relationship between Brooks Range evolution and regional Arctic tectonic events such as the opening of the Canada Basin.