New geochronological evidence for the timing of early Tertiary ridge subduction in southern Alaska

• Main Authors: Parrish, Randall, Bradley, Dwight C, Clendenen, William, Lux, Daniel, Layer, Paul W, Heizler, Matthew, Donley, D Thomas
• Other Authors: Kelley, Karen D., Gough, Larry P.
• Format: Other Non-Article Part of Journal/Newspaper
• Language: English
• Published: U.S. Geological Survey 2000
• Subjects: /dk/atira/pure/core/subjects/earthsci; Earth Sciences; Kodiak; Alaska
• Online Access: https://researchportal.port.ac.uk/portal/en/publications/new-geochronological-evidence-for-the-timing-of-early-tertiary-ridge-subduction-in-southern-alaska(64a10ab9-7ebb-4ff3-a5e1-def920da322e).html; http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.689.9338&rep=rep1&type=pdf#page=12

We present new U/Pb (monazite, zircon) and 40 Ar/ 39 Ar (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 11522 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.