Heavy mineral provenance and paleomagnetic studies of Mesozoic rocks in the Gold Beach terrane, southwestern Oregon, USA

We present detrital mineral and paleomagnetic data from the Gold Beach terrane of southwestern Oregon, USA, that supports its large-magnitude northward translation along the North American margin in the Late Cretaceous. Detrital zircon and titanite were gathered from Late Jurassic−Late Cretaceous aged sandstones and indicate a shift in sediment sources over time. Zircon Hf isotopes in Jurassic grains (200−144 Ma) yield positive ε_Hf(i) values (+15 to +6), whereas Late Cretaceous grains (100−90 Ma) have a wide range of values spanning 20 epsilon units (+11 to −12). Trace-element abundances in detrital zircons show increasing U/Yb and Eu/Eu* with decreasing age. Detrital titanite Nd isotopes mimic zircon Hf isotopes and show ε_Nd(i) values ranging from +8 to +1 in Jurassic aged grains and +5 to −9 in Late Cretaceous grains. Gold Beach titanites are primarily of magmatic origin and are derived from felsic sources, while others have trace element chemistry revealing metamorphic sources.

Paleomagnetic results from the Late Cretaceous Houstenaden Creek Formation pass fold tests with a tilt-corrected mean of D = 130°, I = 70°, n = 12, k = 10, and α₉₅ = 14.4°. The directions have a widely streaked distribution along a small-circle path due to local rotations of blocks between sites. The tilt-corrected, inclination-only mean is I = 59°, n = 12, k = 58, α₉₅ = 4.4°, which yields a Late Cretaceous paleolatitude of 41° ± 4°N. Comparing these results with a Late Cretaceous reference for North America shows an expected paleolatitude of 47°N, resulting in an estimate of 750 ± 500 km of displacement and ∼100° of clockwise rotation. This estimate is consistent with detrital mineral results that indicate continentally derived sources in southern California, as well as a western source offshore of the Late Cretaceous North American margin. We conclude that northward translation of the Gold Beach terrane from southernmost California occurred during the Late Cretaceous and that it was near its present location in southwestern Oregon by the Eocene.