Apatite fission track evidence for paleocene and oligocene uplift events in the northeastern Brooks Range, Alaska

Abstract

Abstract Apatite fission track analysis data from outcrop samples of clastic sedimentary rocks collected from two major areas in the northeastern Brooks Range (NEBR) in the Arctic National Wildlife Refuge of Alaska (ANWR) constrain the timing of uplifts within an advancing deformation front. Eighteen samples from a Permian to Early Cretaceous section at Bathtub Ridge have a range in apparent apatite fission track ages from 49 ± 10 to 74 ± 15 Ma (2σ errors) with a mean value of 62 Ma. Within two sigma errors, all 18 samples define an apparent age of 58–60 Ma. Track lengths are long (mean length 14–15 μm) with tight distributions (standard deviation Seven samples from the Arctic Creek area located 75 km to the northwest all possess apparent apatite fission track ages ranging from 31 ± 7 to 40 ± 15 Ma (2σ errors) with a mean value 37 Ma. Mean track lengths are all long (> 14 μm) with standard deviations between 1.3 and 2.1 μm. These results indicate that previously existing fission tracks were annealed prior to rapid uplift of several kilometers and erosion of the section subsequent to 37 Ma. These apatite fission track data show conclusively that the events responsible for building the NEBR decrease in age from south to north. When deformation was ending throughout most of the Brooks Range during Earliest Tertiary, Bathtub Ridge was being rapidly uplifted. During the Oligocene, the deformation front had progressed northward resulting in the rapid uplift of the Arctic Creek exposures.