Paper No. 4
Presentation Time: 9:00 AM-6:00 PM

DYNAMIC OF OROGENIC PROCESSES IN THE BROOKS RANGES, ALASKA : INSIGHTS FROM LOW T THERMOCHRONOLOGY


BIGOT-BUSCHENDORF, Maelianna1, FILLON, Charlotte1, MOUTHEREAU, Frederic1, LABROUSSE, Loic1, AUXIETRE, Jean-Luc2, WARTES, Marwan3, MOORE, Thomas E.4 and VAN DER BEEK, Peter5, (1)iSTeP, UPMC Paris 6, 4, place Jussieu case 129, Paris, 75005, France, (2)E&P Exploration New Business, Total SA, 2, place J.Millier, Paris La Defense, 92078, (3)Department of Natural Resources, Alaska Geological Survey, 3354 College Rd, Fairbanks, AK 99709-3707, (4)U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, (5)ISTerre, CNRS, U. Grenoble I, BP 53, 1381 rue de la Piscine, Grenoble, 38041, France, loic.labrousse@upmc.fr

The Brooks Ranges, northern Alaska, result from the Mesozoic collision of continental arcs with the Arctic margin and Tertiary retroarc thrusting emmanating from the southern Alaska margin. The exhumation associated with formation of topography and the foreland basin infill both indicate the formation of an orogenic wedge from 160 Ma onward. During the development of the mountain belt, discrete events of rapid exhumation occurred at ~140-120, 100, 60, 45, 35, 25 Ma, correlated to changes in tectonic configuration and in the subduction rate and/or geometry. The cause of the most recent exhumation history of the Brooks Ranges is probably related to the subduction far to the south along the southern Alaska margin, perhaps possible transcurrent movements in Beaufort Sea and also climate variations that have not been assessed yet.

Our study aims at bringing new constraints to the recent tectonic stages in the Brooks Ranges through low temperature thermochronology (U-Th)/He on apatites along the TACT profile from the Ruby Mountains to the North Slope , with special focus on basement lithologies (in the Ruby Mountains and the Schist belt), as well as detrital units ranging from the Devonian (Kanayut Conglomerate) to Cretaceous (Torok, Nanushuk formations). Preliminary results show that most of the topography was acquired early along the TACT profile in the Brooks Ranges (from 100 Ma in the Endicott mountains to 25 Ma in the Doonerak window), yielding low exhumation and erosion rates for that period. Thermokinematic modelling of the main thrust activation sequences shows that a thick-skinned out-of-sequence thrust system must have been active from 30 to 15 Ma along the TACT, and from 40 to 15 in the Shublik mountain.

Unlike in the present day Elias mountain, Arctic climate throughout the late Mesozoic to Early Cenozoic times seems to have inhibited rather than enhanced exhumation in the Brooks Ranges fold-and-thrust belt.

At term, the comparison of this evolution with the tectonic histories of the Pacific subduction in the south and the Arctic Ocean in the north allows us to discuss the balance between coupling with the subduction, heritage from the Arctic margin and surface processes in the Arctic.