U-Pb Geochronology of Volcanic Rocks from the Jurassic Talkeetna
The Geological Society of America Special Paper 43 1 2007 U-Pb geochronology of volcanic rocks from the Jurassic Talkeetna Formation and detrital zircons from prearc and postarc sequences: Implications for the age of magmatism and inheritance in the Talkeetna arc Jeffrey M. Amato* Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA Matthew E. Rioux* Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA Peter B. Kelemen Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA George E. Gehrels Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Peter D. Clift School of Geosciences, University of Aberdeen, Aberdeen, UK Terry L. Pavlis Department of Geological Sciences, University of Texas, El Paso, Texas 79968, USA Amy E. Draut Department of Earth Sciences, University of California, Santa Cruz, California 95064, USA ABSTRACT Six samples collected from pre-, syn-, and post-Talkeetna arc units in south- central Alaska were dated using single-grain zircon LA-MC-ICP-MS geochronology to assess the age of arc volcanism and the presence and age of any inherited compo- nents in the arc. The oldest dated sample comes from a volcanic breccia at the base of the Talkeetna Formation on the Alaska Peninsula and indicates that initial arc volcan- ism began by 207 ? 5 Ma. A sedimentary rock overlying the volcanic section in the Talkeetna Mountains has a maximum depositional age of 467 Ma. This is in agree- ment with biochronologic ages for the top of the Talkeetna Formation, suggesting that the Talkeetna arc was active for ca.
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