From Deposition to Deformation Within an Accretionary Suture Zone: An Example from the Clearwater and Talkeetna Mountains, Alaska Range Suture Zone
Abstract
In this study, detailed structural analysis is combined with zircon geochronology and Hf isotopic studies of zircon to understand the evolution of the Alaska Range suture zone, in the Clearwater and Talkeetna Mountains. Detrital zircon U/Pb ages and Hf-isotopes of zircon have been used to constrain the provenance and maximum depositional age (MDA) of three distinct tectonostratigraphic packages. These packages from oldest to youngest are: the Kahiltna assemblage, a fine-grained turbiditic package with age distributions strongly dominated by the MDA populations with peaks of ∼150-160 Ma; the Maclaren Glacier metamorphic belt, upper amphibolite facies metasedimentary rocks with MDA’s of 95-107 Ma and numerous pre-Mesozoic ages; and the Pass Creek conglomerate, a boulder to cobble conglomerate with numerous pre-Mesozoic zircon ages and MDA’s from 80-141 Ma. These ages show that metamorphic rocks of the Maclaren Glacier metamorphic belt are derived from North American sources, whereas the Kahiltna assemblage, is derived from local sources within the Wrangellia composite terrane. These two packages are juxtaposed across the Valdez Creek shear zone, a ductile top-to-the south thrust with an inverted metamorphic gradient, with the third package the Pass Creek conglomerate being deposited after closure of the suture between the Maclaren Glacier metamorphic belt and the Kahiltna assemblage. Zircon crystallization ages of igneous rocks are used to constrain the timing of major deformation events that juxtaposed these distinct stratigraphic sequences. When these datasets are examined together the Valdez Creek shear zone was found to represent a major suture between North America and the Wrangellia composite terrane, with the closing of the intervening ocean basin occurring between 90 and 85 Ma.
Degree
M.S.
Advisors
Andronicos, Purdue University.
Subject Area
Geology|Geochemistry
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