Evolving heavy mineral assemblages reveal changing exhumation and trench tectonics in the Mesozoic Chugach accretionary complex, south-central Alaska
- 9 March 2012
- journal article
- Published by Geological Society of America in GSA Bulletin
- Vol. 124 (5-6), 989-1006
- https://doi.org/10.1130/b30594.1
Abstract
The Gulf of Alaska is one of the largest accretionary complexes on Earth. In this study, we examined the earliest phase of accretion in the Mesozoic McHugh Complex and Valdez Groups, exposed in SE Alaska. The oldest preserved fragment, the Mesomélange assemblage, is Jurassic (ca. 160–140 Ma) and consists of an ∼3-km-thick structural package of strongly deformed shaley materials 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 Talkeetna 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 provided 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 initiation of Shimanto Complex accretion in Japan and can be understood as primarily linked to sediment supply driven by plate-margin tectonics rather than climatically induced erosion onshore.Keywords
This publication has 52 references indexed in Scilit:
- Detrital zircon ages from the Chugach terrane, southern Alaska, reveal multiple episodes of accretion and erosion in a subduction complexGeology, 2010
- Crustal redistribution, crust–mantle recycling and Phanerozoic evolution of the continental crustEarth-Science Reviews, 2009
- Subduction erosion of the Jurassic Talkeetna-Bonanza arc and the Mesozoic accretionary tectonics of western North AmericaGeology, 2005
- Seismic reflection imaging of two megathrust shear zones in the northern Cascadia subduction zoneNature, 2004
- Metamorphism and near-trench plutonism during initial accretion of the Cretaceous Alaskan forearcJournal of Geophysical Research: Solid Earth, 1994
- Characterisation of intra‐oceanic magmatic arc source terranes by provenance studies of derived sedimentsNew Zealand Journal of Geology and Geophysics, 1991
- Provenance mixing in an intraoceanic subduction zone: Tonga Trench-Louisville Ridge collision zone, southwest PacificSedimentary Geology, 1990
- Subduction of a Late Cretaceous Seamount of the Louisville Ridge at the Tonga Trench: A model of normal and accelerated tectonic erosionTectonics, 1989
- Late cretaceous pelagic sediments, volcanic ASH and biotas from near the Louisville hotspot, Pacific Plate, paleolatitude ∼42°SPalaeogeography, Palaeoclimatology, Palaeoecology, 1989
- Subduction-channel model of prism accretion, melange formation, sediment subduction, and subduction erosion at convergent plate margins: 1. Background and descriptionPure and Applied Geophysics, 1988