Rock and age relationships within the Talkeetna forearc accretionary complex in the Nelchina area, southern Alaska

• Main Authors: Barefoot, John, Nadin, Elisabeth S, Newberry, Rainer, Camacho, Alfredo
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: NRC Research Press (a division of Canadian Science Publishing) 2019
• Subjects: glacier; Alaska
• Online Access: http://hdl.handle.net/1807/99871; http://www.nrcresearchpress.com/doi/abs/10.1139/cjes-2018-0268

Subduction-zone processes are challenging to study because of the rarity of good exposures and the complexity of rock relationships within accretionary prisms. We report results of field mapping and petrographic, geochemical, and geochronological analyses of McHugh Complex accretionary prism mlange in south-central Alaska that was recently exposed due to retreat of the Nelchina Glacier. Our new mapping and analyses of the mlange, as well as adjacent Talkeetna arc intrusives, suggests that the previously mapped trace of the Border Ranges fault should shift northward in this location. Detailed petrographic analysis places this mlange exposure with the Potter Creek assemblage of the McHugh Complex. Blocks of pillow lavas within the mlange have both MORB and intra-plate geochemical affinity, attesting to the complex relations of subduction-zone inputs in an alternating erosive–accretionary margin. A new zircon U-Pb age and geochemical analyses of a set of felsic dikes that crosscut the accretionary sequence provide constraints on the regional tectonic evolution, including near-trench plutonism associated with the migration of a subducting spreading ridge along the southern Alaska margin in Paleocene–Eocene time. The McHugh section and crosscutting dikes in this location are pervasively hydrothermally altered, which we attribute to elevated temperatures related to ridge subduction. Late-stage motion along the Border Ranges fault system, which is also recorded in the area, may also have contributed to the widespread alteration. Our data indicate that the Talkeetna volcanic arc and associated accretionary prism sediments were in their current configuration by 55 Ma. The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author.