Constraints on the Mesozoic and Cenozoic Thermotectonic Evolution of the Northern Brooks Range and the North Slope Foreland Basin from Fission Track Thermochronology

By

P.B. O’Sullivan (Syracuse University), T.E. Moore, C.J. Potter (U.S. Geological Survey), and W.K. Wallace (University of Alaska, Fairbanks)

Zircon and apatite fission track results from Upper Devonian through Upper Cretaceous sedimentary rocks help resolve the timing of uplift and denudation along the northern flank of the Brooks Range orogen, the northern foothills belt, and the southern flank of the adjoining North Slope foreland basin. Zircon results from outcrop samples within the orogen record cooling below paleotemperatures <240 degrees C at ~140 Ma, ~120 Ma, ~60 Ma, and ~45 Ma, whereas apatite results record rapid cooling below paleotemperatures <110 degrees C during discrete episodes at ~100 Ma, ~60 Ma, ~45 Ma, and ~25 Ma. Within the northern foothills and adjoining foreland basin, zircon results from outcrop samples record provenance cooling ages with distinct grain-age populations at ~160 Ma, ~140 Ma, and 120 Ma, whereas apatite results record rapid cooling below paleotemperatures <110 degrees C at ~100 Ma, ~60 Ma, ~45 Ma, and ~25 Ma. To the north within the basin, apatite results from subsurface samples indicate that they were exposed to maximum paleotemperatures in the Late Cretaceous to early Paleocene as a result of subsidence and burial by Upper Jurassic and Cretaceous sedimentary rocks. Rapid cooling from these elevated paleotemperatures subsequently occurred at ~60 Ma, ~45 Ma, and ~25 Ma. These episodes of rapid cooling are interpreted to reflect km-scale erosional denudation resulting from uplift due to structural thickening during episodes of shortening within the Brooks Range and its foreland basin. However, additional work is required to document which structures in the central Brooks Range were active during the 45 and 25 Ma events.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.