T56 The Life and Death of Mobile Belts along the North American Cordillera: Advances in Understanding the Long- Term Construction of Continental Margins (Posters)

Sunday, 27 October 2013
9:00 AM - 6:30 PM
Hall D

U-PB AND HF ISOTOPIC ANALYSES OF DETRITAL ZIRCONS FROM THE TAKU TERRANE, SOUTHEAST ALASKA

Paper number: T56-11
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

In the southeast Alaskan panhandle, amidst the folded, faulted, and accreted terranes, sits the Taku terrane. Previous workers have defined, and re-defined the terrane, and it is currently identified as a package of 3 units; Carboniferous(?)-Permian strata of the Windham Group, Permian strata of the Gastineau Group, and Triassic strata of the Perseverance Group. These strata are structurally overlain to the east by the Yukon-Tanana terrane (YTT) and structurally overlie Jurassic-Cretaceous strata of the Gravina belt to the west. For this study we have collected 583 U-Pb ages and 74 Hf isotope determinations from detrital zircon grains of six samples in locations between Juneau and Ketchikan. Two samples from the Windham Group yield predominantly 360-400 Ma grains (peak age of 383 Ma) and one grain of ~437 Ma. Epsilon Hf values for these grains are highly variable, ranging from +16 to -3. One sample from the Gastineau Group yields a similar age group of 350-395 Ma (age peak of 370 Ma). Two samples of the Perseverance Group have a dominant age group of 340-385 Ma (peak age of 363 Ma) and subordinate age groups of 410-460 Ma and 220-290 Ma. Epsilon Hf values for the 340-385 Ma grains are highly variable, ranging from +10 to -18, whereas the 410-460 Ma grains are all juvenile (epsilon Hf values of +7 to +14). One additional sample of the Gastineau Group yields very different ages, with main age groups of 275-300 Ma (peak age of 292 Ma) and 400-460 Ma (peak age of 435 Ma). Hf isotopic compositions of the 400-460 Ma grains are highly juvenile (+10 to +16), whereas compositions for the 275-300 Ma grains are intermediate (+5 to +10) in value. Collectively these data support previous suggestions that most sediment in the Taku terrane was shed from the Yukon-Tanana terrane, and also demonstrate that some sediment was derived from the Alexander terrane during Permian and Triassic time.