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Blythe, A.E., 1992

Central and western Brooks Range, Alaska, tectonic evolution: Fission-track and 40Ar/39Ar thermochronometry

Bibliographic Reference

Blythe, A.E., 1992, Central and western Brooks Range, Alaska, tectonic evolution: Fission-track and 40Ar/39Ar thermochronometry: Ithaca, New York, Cornell University, Ph.D. dissertation, 234 p., illust., maps.


The first chapter of this dissertation is a study of the central Brooks Range (BR), Alaska, thermal history from apatite and zircon fission track and white mica 40Ar/39Ar analyses. The data indicate that slow cooling had begun by ~210 Ma. An increase in the cooling rate occurred from ~130 to 95 Ma, probably as the result of deformation during opening of the Canada basin; uplift/erosion of southern BR blueschist at that time may have been the result of a change in subducting-slab dip. Extensional faulting on the BR southern margin appears to have occurred at ~113 Ma. Rapid cooling is indicated at ~60 Ma throughout the central BR, and at ~30 Ma in the Doonerak Window; uplift of 2-3 km at these times is inferred. Cooling episodes at these times coincide with, and are probably related to, episodes of magmatism in southern Alaska. The second chapter is a study of the Yukon-Koyukuk basin (YKB) and Ruby terrane (RT), on the southern margin of the BR. Fission track (FT) and 40Ar/39Ar analyses of the Hot Springs and Jim River plutons indicate rapid cooling through 300 degrees C by 95 and 107 Ma and through 60 degrees C by 95 and 92 Ma, and suggest that major extension had ended by ~95 Ma. Kanuti pluton analyses indicate cooling through ~300 degrees C at ~107 Ma, and reheating during Tertiary volcanism. A 39 Ma apatite fission track age from a Cretaceous conglomerate is attributed to either Tertiary deformation or volcanism. The third chapter is a study of the Noatak basin (NB) in the western BR. The NB may be a remnant of a Carboniferous aulacogen; the distribution of sulfides, igneous rocks, and a microcline-bearing arkose provide evidence for an aulacogen in the western BR region. NB gravity data is consistent with this interpretation. Ophiolites bordering the NB might have originated in small ocean basins formed in the aulacogen region during the Jurassic. Deformation during Early Cretaceous arc-continent collision overprinted aulacogen structures. Lineaments and Cenozoic sedimentation suggest that recent movement has occurred along aulacogen-related faults.

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