GEOLOGICAL EVIDENCE FROM THE DOONERAK FENSTER AND THE ENDICOTT MOUNTAINS ALLOCHTHON OF THE CENTRAL BROOKS RANGE, ALASKA: INSIGHTS INTO THE ASSEMBLY OF THE ARCTIC ALASKA TERRANE

In the Doonerak fenster of the central Brooks Range, AK, an autochthonous assemblage of early Paleozoic volcanic and sedimentary rocks, the Apoon assemblage, has putative connections with the early phases of the Caledonian orogeny. During the formation of the Mesozoic-Cenozoic Brookian fold-thrust belt, the Endicott Mountains allochthon, an Upper Devonian-Triassic package of siliciclastic and carbonate rocks, was displaced northward and juxtaposed above of the Apoon assemblage in the form a foreland-dipping duplex.

New whole-rock major and trace element geochemical analyses conducted on the Apoon volcanic rocks show somewhat variable patterns, but all samples are consistent with an arc/subduction-related tectonic setting. U-Pb detrital zircon ages from volcaniclastic portions of the Apoon assemblage highlight a prominent unimodal 440-530 Ma population, which is in concert with previous U-Pb geochronology from the Apoon assemblage. A similar prominent detrital population is present in the siliciclastic units of the Endicott Mountains allochthon. This could imply that the Endicott Mountains allochthon units were sourced by recycling the volcanic and volcaniclastic rocks of the Apoon assemblage; however, the allochthonous units bear detrital populations that are absent within the Apoon assemblage and are similar to those seen along the Canadian Arctic Islands, Svalbard, eastern Greenland, and possibly northern Baltica. This recorded shift in provenance likely corresponds with the closure of the northern Iapetus Ocean and the amalgamation of the Arctic Alaska terrane.