LATE MESOZOIC AND CENOZOIC THERMOTECTONIC EVOLUTION OF THE CENTRAL BROOKS RANGE AND ADJACENT NORTH SLOPE FORELAND BASIN, ALASKA - INCLUDINGFISSION-TRACK RESULTS FROM THE TRANS-ALASKA CRUSTAL TRANSECT (TACT)

Apatite fission track data are used to evaluate the thermal and tecton ic history of the central Brooks Range and the North Slope foreland ba sin in northern Alaska along the northern leg of the Trans-Alaska Crus tal Transect (TACT). Fission track analyses of the detrital apatite gr ains in most sedimentary units resolve the timing of structures and de nudation within the Brooks Range, ranging in scale from the entire mou ntain range to relatively small-scale folds and faults. Interpretation of the results indicates that rocks exposed within the central Brooks Range cooled rapidly from paleotemperatures 110 degrees to 50 degrees C during discrete episodes at similar to 100+/-5 Ma, similar to 60+/- 4 Ma, and similar to 24+/-3 Ma, probably in response to kilometer-scal e denudation. North of the mountain front, rocks in the southern half of the foreland basin were exposed to maximum paleotemperatures 110 de grees C in the Late Cretaceous to early Paleocene as a result of buria l by Upper Jurassic and Cretaceous sedimentary rocks. Rapid cooling fr om these elevated paleotemperatures also occurred due to distinct epis odes of kilometer-scale denudation at similar to 60+/-4 Ma, 46+/-3 Ma, 35+/-2 Ma, and similar to 24+/-3 Ma. Combined, the apatite analyses i ndicate that rocks exposed along the TACT line through the central Bro oks Range and foreland basin experienced episodic rapid cooling throug hout the Late Cretaceous and Cenozoic in response to at least three di stinct kilometer-scale denudation events. Future models explaining oro genic events in northern Alaska must consider these new constraints fr om fission track thermochronology.