DETRITAL ZIRCON AND PALEOMAGNETIC DATA FROM THE GOLD BEACH TERRANE SUPPORT BAJA BC HYPOTHESIS

We undertook a study of the Cretaceous Gold Beach terrane, exposed west of the Klamath Mountains along the SW Oregon coast, and specifically the Late Cretaceous (Campanian) Houstenaden Creek Fm. The detrital zircon U/Pb age and Hf isotopic signature for three sites were analyzed at Washington State University. U/Pb ages vary between 84.8 +/- 1.1 Ma to 263 +/- 2.8 Ma, with major peaks at ~90 Ma, ~105, ~135 Ma, and ~165 Ma. In general, the Late Jurassic to Early Cretaceous ages are associated with positive epsilon Hf values between 2 and 15, indicating a more juvenile source of magma. The younger Early Cretaceous zircons, in contrast, have more variable Hf values, between -12 and +10, with the more negative values obtained from the youngest detrital grains, indicating a more evolved crustal input. Paleomagnetic results from 12 sites of the Houstenaden Creek Fm have well-defined directions, with both normal and reverse-polarity magnetizations. The results pass the paleomagnetic tilt-test with a peak in clustering at 100% untilting. The tilt corrected mean is Dec = 78, I = 55, k=25, a95=8, yielding a Late Cretaceous paleolatitude of 36 N. These directions indicate very large (100 degrees) CW rotation of the Gold Beach rocks relative to North America. Interpretation of the paleolatitude requires an evaluation of the effects of possible inclination error, conducted using the set of specimen level directions and the E/I method of Tauxe and Kent 2004. The corrected inclinations are between 51 and 65 degrees - placing the Gold Beach terrane at paleolatitudes between 36 and 47 N. Combining these data indicates post ~85 Ma northward translations of 1000-1500 km to their present location with respect to North America. We discuss this new data in the context of the proposal, from Bourgeois and Dott (1985), that the Houstenaden Creek Fm of the Gold Beach terrane received sediment from multiple sources and underwent northward coastwise translation.