New geochronological evidence for the timing of early Tertiary ridge subduction in southern Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998
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Abstract
We present new U/Pb (monazite, zircon) and 40Ar/39Ar (biotite, amphibole) ages for 10 Tertiary plutons and dikes that intrude the Chugach–Prince William accretionary complex of southern Alaska. The Sanak pluton of Sanak Island yielded ages of 61.1±0.5 Ma (zircon) and 62.7±0.35 (biotite). The Shumagin pluton of Big Koniuji Island yielded a U/Pb zircon age of 61.1±0.3 Ma. Two biotite ages from the Kodiak batholith of Kodiak Island are nearly identical at 58.3±0.2 and 57.3±2.5 Ma. Amphibole from a dike at Malina Bay, Afognak Island, is 59.3±2.2 Ma; amphibole from a dike in Seldovia Bay, Kenai Peninsula, is 57.0±0.2 Ma. The Nuka pluton, Kenai Peninsula, yielded ages of 56.0±0.5 Ma (monazite) and 54.2±0.1 (biotite). Biotite plateau ages are reported for the Aialik (52.2±0.9 Ma), Tustumena (53.2±1.1 Ma), Chernof (54.2±1.1 Ma), and Hive Island (53.4±0.4 Ma) plutons of the Kenai Peninsula. Together, these new results confirm, but refine, the previously documented along-strike diachronous age trend of near-trench magmatism during the early Tertiary. We suggest that this event began at 61 Ma at Sanak Island, 2-4 m.y. later than previously supposed. An intermediate dike near Tutka Bay, Kenai Peninsula, yielded a hornblende age of 115±2 Ma. This represents a near-trench magmatic event that had heretofore gone unrecognized on the Kenai Peninsula; correlative Early Cretaceous near-trench plutons are known from the western Chugach Mountains near Palmer.
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | New geochronological evidence for the timing of early Tertiary ridge subduction in southern Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998 |
| Series title | Professional Paper |
| Series number | 1615 |
| DOI | 10.3133/70180636 |
| Year Published | 2000 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Publisher location | Denver, CO |
| Contributing office(s) | Alaska Science Center, Alaska Science Center Geology Minerals, Central Mineral and Environmental Resources Science Center |
| Description | 17 p. |
| Larger Work Type | Report |
| Larger Work Subtype | USGS Numbered Series |
| Larger Work Title | Geologic studies in Alaska by the U.S. Geological Survey, 1998 (Professional Paper 1615) |
| First page | 5 |
| Last page | 21 |
| Country | United States |
| State | Alaska |
| Google Analytic Metrics | Metrics page |