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

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Six samples collected from pre-, syn-, and post-Talkeetna arc units in southcentral 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 components 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 volcanism began by 207 ± 5 Ma. A sedimentary rock overlying the volcanic section in the Talkeetna Mountains has a maximum depositional age of <167 Ma. This is in agreement with biochronologic ages for the top of the Talkeetna Formation, suggesting that the Talkeetna arc was active for ca. 40 m.y. Three samples from interplutonic screens and roof pendants in the Jurassic batholith on the Alaska Peninsula provide information about the tectonic setting of Talkeetna arc magmatism. All three samples contain Paleozoic to Proterozoic zircons and require that arc magmas on the Alaska Peninsula intruded into detritus that contained older continental zircons. This finding is distinct from observations from eastern exposures of the arc in the Chugach and Talkeetna Mountains, where there is only limited evidence for pre-Paleozoic zircons, and it suggests that there were along-strike variations in the tectonic setting of the arc. Copyright © 2007 The Geological Society of America.

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Special Paper of the Geological Society of America

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