2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 179-12
Presentation Time: 11:25 AM

OXYGEN AND HAFNIUM ISOTOPE GEOCHEMISTRY OF ZIRCON, QUARTZ, AND GARNET FROM THE NEAR-TRENCH CRAWFISH INLET AND KRESTOF PLUTONS, BARANOF ISLAND, ALASKA


ROIG, Claudia I.1, CAVOSIE, Aaron J.1, DAVIDSON, Cameron2, GARVER, John I.3 and VALLEY, John W.4, (1)Department of Geology, University of Puerto Rico, Po Box 9000, Mayaguez, PR 00681, (2)Department of Geology, Carleton College, 1 N College St, Northfield, MN 55057, (3)Geology Department, Union College, Olin Building, Schenectady, NY 12308-2311, (4)Department of Geoscience, University of Wisconsin, Madison, WI 53706, claudia.roig@upr.edu

The Paleocene to early Eocene Sanak–Baranof plutonic belt (SBPB) is a 2100 km series of near-trench plutons that intruded the entire Upper Cretaceous to Paleocene Chugach–Prince William terrane accretionary complex along the continental margin of southeast Alaska between 61-47 Ma. This study presents new oxygen and hafnium isotope analyses, and U/Pb geochronology on the Crawfish Inlet Pluton and the Krestof Pluton, from the eastern part of the Sanak-Baranof Belt, to further evaluate the hypothesis of a crust vs. mantle origins for the SBPB. The goals of this project include: correlating δ18O with available ε-Hf (Zrc) and U/Pb age (Zrc), and using thermometry by calculating inter-mineral O fractionations. Values of δ18O (Zrc) range from 6.18 ± 0.12‰ (2σ) to 7.48 ± 0.12‰, and exhibit evidence for the incorporation of recycled crust, as they uniformly plot above the range for mantle equilibrated zircon. U/Pb ages from seven samples within the CIP and one sample from a small satellite sill (CP13-08) range from 47.3±1.2 to 53.1±0.8 Ma. Hf isotopes collected from four samples within the CIP yield ε-Hf values ranging from +18.2 ± 1.5 (1σ) at 47.4 Ma to +0.8 ± 1.5 (1σ) at 54.0 Ma, indicating a distinct trend within the CIP. The results show a strong correlation between ε-Hf and O indicating that the more primitive (juvenile) granitoid zircons with higher ε-Hf values record the least evolved oxygen isotope ratios, with decreasing importance of crustal recycling during the genesis of these granitoids with time.
Handouts
  • Roig_et_al_GSA_2014.pdf (2.0 MB)