Intraarc basin development in a continental arctransform transition

Intra-arc basin development in a continental arc-transform transition zone, Jeff Trop, Bucknell University Undergraduate students – M. Ryan Delaney, R. Daniel Heuer, and John Witmer Stratigraphic analysis of the Wrangell volcanic field in Alaska provides a framework for evaluating spatial and temporal variations in magmatism, intra-arc basin development, and accretionary tectonics along the northern Pacific margin. Sedimentology: measured stratigraphic sections document upsection transitions from alluvial-fluvial -lacustrine deposition to emplacement of mainly volcanic strata. Expansion of intra-basinal volcanic centers prompted progradation of vent-proximal alluvial fans and volcanic centers across swampy fluvial-lacustrine environments. Section 13 Provenance - U-Pb detrital zircon data from sandstone show three dominant peaks: 180 -135, 97 -70, and 12 -9 Ma that indicate erosion of coeval volcanic centers and remnant arc rocks. Geochronology - Tuffs yield 12 -11 Ma U-Pb zircon ages. 12 -9 Ma zircon ages from sandstone overlap published ages from nearby volcanic successions. Ongoing Ar-Ar geochronology of lavas will further constrain depositional ages. Geochemistry - Sampled lavas exhibit geochemical compositions typical of subduction-related arc volcanic suites. These lavas define elemental relationships indistinguishable from those observed for a subset of <5 Ma western WVF lavas inferred to have been emplaced in an intra-arc extensional setting. Tectonics – Collectively, our new data demonstrate that intra-arc basin development overlapped with cessation of strike-slip basin development and magmatism in the eastern WVF (ca. 10 Ma) and preceded arc magmatism in the western WVF (ca. 7 -<1 Ma), consistent with diachronous collision of the Yakutat terrane against the northern Pacific margin.