Paleomagnetism of the Resurrection Peninsula, Alaska: Implications for the tectonics of southern Alaska and the Kula‐Farallon Ridge

Abstract

The rocks of the Resurrection Peninsula compose an ophiolite (57±1 Ma) within the vast accretionary prism of the Chugach‐Prince William terrane. Paleomagnetic data from pillow basalt and sheeted dikes of the ophiolite yield a mean paleolatitude of 54°±7°, which implies 13±9° of poleward displacement. The characteristic component of the remanence resides in a Ti‐poor titanomagnetite with a blocking temperature close td 580°C. A positive fold test and the petrology of the magnetic minerals lead us to conclude that the characteristic remanent magnetization (ChRM) in the sheeted dikes originated as a primary thermoremanent magnetization (TRM). We hypothesize that the ChRM of the pillow basalt originated as a chemical remanent magnetization (CRM) acquired soon after formation of the rocks during hydrothermal metamorphism. Structural data indicate polyphase deformation with folding about vertical and horizontal axes. The paleomagnetic data pass a fold test only when we incorporate this interpretation in our structural correction. Geologic relationships lead us to interpret the Resurrection Peninsula ophiolite as a fragment of the extinct Kula‐Farallon ridge that accreted to the Chugach‐Prince William terrane soon after formation. The paleomagnetic paleolatitude indicates that the ridge intersected the North American continental margin in the vicinity of northern Washington in late Paleocene time. The paleostrike of the sheeted dikes (N26°E±12°) shows that the ridge trended NNE. According to current plate tectonic models, if the Chugach‐Prince William terrane moved north with the full coastwise displacement of the Kula plate, the Resurrection Peninsula ophiolite would have arrived at its present position at 45 Ma. This age is perhaps slightly later than that of the terranes that lay immediately inboard (Peninsular and Wrangellia terranes), indicating some relative displacement between those terranes and the Chugach‐Prince William terrane. Such displacement, in turn, agrees with studies which imply a Coast plutonicmetamorphic complex provenance for the Chugach‐Prince William terrane.