MAGNETIC FABRICS, PALEOMAGNETISM, AND U-PB ZIRCON AGES OF CLASTIC MARINE SEDIMENTS: IMPLICATIONS FOR PROVENANCE AND TECTONIC HISTORY OF THE GOLD BEACH TERRANE

Ben van der Pluijm and his research group have made numerous contributions to our understanding of orogenic processes. This body of work is most successful in applications of multidisciplinary studies to such problems. For example, paleomagnetic and magnetic fabric analysis of clastic marine sediments and sedimentary rocks, and associated sedimentary records of orogenic processes such as detrital mineral thermochronology have provided important insights into several orogenic systems.

From the Gold Beach terrane (SW Oregon), paleomagnetic, magnetic fabric, and detrital zircon U/Pb ages can be used to understand the origin and tectonic history of this tectonic unit. Samples collected from the Cape Sebastian, Hunters Cove, and Houstenaden Creek Formations (Liner, 2005) have a paleomagnetic signal that is of variable quality- with only the sediments of the Houstenaden Creek Fm yielding consistent paleomagnetic results. All of the units, however, have well-defined magnetic fabrics. These will be examined using methods of Taira (1989) and Novak et al (2014) to use AMS fabric shape, and the imbrication-angle of the AMS foliation to classify depositional environment. The AMS orientations also yield sediment transport directions for these units. Paleomagnetic results from 7 sites of the Houstenaden Creek Fm pass both fold and reversals tests- but have a streaked distribution of site mean directions indicating local rotations (Liner, 2003). The tilt corrected, inclination-only mean I = 55, yielding a late Cretaceous paleolatitude of 36 N. Correcting for rotation using the site-mean declinations, the AMS results all indicate a consistent SW-directed sediment transport direction. U-Pb ages of 100 detrital zircons from the Houstenaden Creek Fm have two distinct peak in their age distribution- one at 160-170 Ma, and the other at 85-100 Ma. Combined, the paleomagnetic data, sediment transport directions from the AMS, and detrital zircon U-Pb ages would be consistent with detritus sourced from a number of possibilities, including Klamath, Coast Ranges, or Sierra Nevada plutonic sources. Additional data- Hf isotopes, and possible future work including thermochronology of the detritus in the Gold Beach terrane will enable the tectonic interaction with this terrane and the NA margin to be better understood.