by Peter Clift
Published in Geological Society of America Bulletin 124(5/6), 989–1006, doi: 10.1130/B30594.1.
Full authorship is Clift, P.D., Wares, N.M., Amato, J.M., Pavlis, T.L., Hole, M.J., Worthman, C. and Day, E.
The Gulf of Alaska is one of the largest ac- cretionary complexes on Earth. In this study, we examined the earliest... more
The Gulf of Alaska is one of the largest ac- cretionary complexes on Earth. In this study, we examined the earliest phase of accretion in the Mesozoic McHugh Complex and Val- dez Groups, exposed in SE Alaska. The old- est preserved fragment, the Mesomélange assemblage, is Jurassic (ca. 160–140 Ma) and consists of an ~3-km-thick structural package of strongly deformed shaley materi- als with slices of oceanic cherts and basalts. Heavy minerals indicate dominant erosion from a magmatic arc source uplifted after the collision of the Wrangellia and the Tal- keetna oceanic arc. A tectonic erosion event affected the forearc just prior to ca. 120 Ma and was likely caused by seamount collision, ridge subduction, or both. This was followed at 105 Ma by mass wasting of sandstone and conglomerates, preserved as the Graywacke- Conglomerate assemblage (ca. 105–83 Ma). Heavy minerals indicate continued flux from arc sources, but with significant changes suggesting a larger, more diverse catchment area. Erosion of deeper crustal sources pro- vided high-Mg diopside and garnets to the trench. Faster sediment flux was caused by rock uplift triggered by final accretion of the Wrangellia-Peninsula terrane to North America. The start of large-scale accretion in Alaska roughly coincided with the initia- tion of Shimanto Complex accretion in Japan and can be understood as primarily linked to sediment supply driven by plate-margin tec- tonics rather than climatically induced ero- sion onshore.
Download (.pdf) 