OVERPRINT MAGNETIZATIONS IN SUPPORT OF NORTHWARD DISPLACEMENT OF THE CHUGACH-PRINCE-WILLIAM-TERRANE, ALASKA

Widespread discrepancies between geologic and paleomagnetic estimates of northward displacement are ubiquitous in reconstructions of the North American Cordillera. In southern Alaska, this discrepancy persists into Paleogene time. Paleomagnetic data indicate that the Mesozoic arc complex of the Southern Alaska terrane was in place by Late Cretaceous-early Tertiary time, while the outboard Mesozoic and Tertiary accretionary complex of the Chugach-Prince William terrane still lay far to the south. The apparent Tertiary displacement of the Chugach-Prince William terrane is difficult to reconcile with most apparent geologic constraints. I studied the paleomagnetism of early Tertiary mafic volcanic rocks from Prince William Sound, Alaska, in an attempt to corroborate the meager paleomagnetic database. I sampled at Knight Island and Glacier Island and found overprint magnetizations. At Knight Island, the paleomagnetic directions are too scattered for tectonic interpretation. At Glacier Island, I found three overprint magnetizations. The type 1 magnetization has a normal direction and is concordant with the expected direction for North America. The type 2N magnetization yields a characteristic direction which is too scattered for tectonic interpretation. The type 2R magnetization is reversed and implies 17-degrees +/- 10-degrees of northward displacement with respect to North America assuming that the magnetization was acquired at 55 Ma and the ophiotite was not subsequently tilted. The type 2R magnetization agrees remarkably well with paleomagnetic results from the nearby Resurrection Peninsula in terms of inferred displacement, paleotrend of the sheeted dike complex, and reversed polarity of magnetization. The type 1 magnetization was subsequently acquired after the Chugach-Prince William terrane arrived in southern Alaska.