Conference proceeding
"Taconic" arc magmatism in the central Brooks Range, Alaska; new U-Pb zircon geochronology and Hf isotopic data from the lower Paleozoic Apoon assemblage of the Doonerak fenster
American Geophysical Union Fall Meeting, Vol.2015
American Geophysical Union 2015 fall meeting
12/2015
Abstract
The Doonerak fenster in the central Brooks Range, AK, exposes an important package of early Paleozoic volcanic and sedimentary rocks called the Apoon assemblage, which are generally interpreted as para-autochthonous basement to the Mesozoic-Cenozoic Brookian fold-thrust belt. Recognition in the 1970's of a major pre-Mississippian unconformity within the window led to correlations between Doonerak and the North Slope (sub-) terrane of the Arctic Alaska Chukotka microplate (AACM); however, the presence of arc-affinity volcanism and the apparent lack of pre-Mississippian deformation in the Apoon assemblage makes this link tenuous and complicates Paleozoic tectonic reconstructions of the AACM. Previous age constraints on the Apoon assemblage are limited to a handful of Middle Cambrian-Silurian paleontological collections and five K-Ar and (super 40) Ar/ (super 39) Ar hornblende ages from mafic dikes ranging from nearly equal 380-520 Ma. We conducted U-Pb geochronologic and Hf isotopic analyses on igneous and sedimentary zircon from the Apoon assemblage to test Paleozoic links with the North Slope and to assess the tectonic and paleogeographic setting of the Doonerak region. U-Pb analyses on detrital zircon from Apoon rocks yield a spectrum of unimodal and polymodal age populations, including prominent age groups of ca. 420-490, 960-1250, 1380-1500, 1750-1945, and 2650-2830 Ma. Hf isotopic data from the ca. 410-490 Ma age population are generally juvenile ( nearly equal 7-10 epsilon Hf), implying a distinct lack of crustal assimilation during Ordovician-Silurian Doonerak arc magmatism despite its proximity to a cratonic source terrane as indicated by an abundance of Archean and Proterozoic zircon in the interbedded siliciclastic strata. These data are in stark contrast to geochronological data from the non-Laurentian portions of the AACM, highlighting a prominent tectonic boundary between Laurentian- and Baltic-affinity rocks at the Doonerak window and implying a link to "Taconic"-age arc magmatism documented along the NE Laurentian margin.
Details
- Title: Subtitle
- "Taconic" arc magmatism in the central Brooks Range, Alaska; new U-Pb zircon geochronology and Hf isotopic data from the lower Paleozoic Apoon assemblage of the Doonerak fenster
- Creators
- J. V Strauss - Department of Earth SciencesC. W HoilandW WardB JohnsonW McClelland
- Resource Type
- Conference proceeding
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2015
- Conference
- American Geophysical Union 2015 fall meeting
- Publisher
- American Geophysical Union
- Alternative title
- AGU 2015 fall meeting
- Language
- English
- Date published
- 12/2015
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240904102771
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