Comment and Reply on "Escape hypothesis for the Stikine block"

Abstract

When stratigraphic, geochemical, and faunal data of Wrangellia and Wallowa-Seven Devils are viewed objectively, the data suggest—but do not require—that the two crustal blocks developed adjacent to one another. Sarewitz (1983) and Rusmore (1987) noted that the geochemical differences between the arclike Wallowa and Cadwallader volcanic rocks vs. the back-arclike Karmutsen volcanics on Wrangellia may be the result of their tectonic setting relative to the arc axis. We disagree with Mortimer's (1986) correlation of Wallowa volcanics with Stikinia volcanics because the subalkalic volcanic rocks of Wallowa are mainly Ladinian in age and compare poorly with the calc-alkalic augite porphyry of Carnian- Norian age that is typical of Stikine. Newton (1983) reported that Late Triassic molluscan fauna from the Wallowa terrane are most similar to those collected from the Wrangell Mountains. As addressed below, paleomagnetic data do not constrain Wallowa-Wrangellia-Stikine correlations. It appears, therefore, that faunal ties and timing of volcanism indicate that the Wallowa terrane is more similar to Wrangellia than to Stikine, and we incorporate this correlation into our model until direct evidence can support or deny it.