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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.