EVALUATION OF PALEOMAGNETIC INCLINATION ERROR ON PALEOMAGNETIC RESULTS FROM THE KARHEEN FORMATION- IMPLICATIONS FOR THE DEVONIAN PALEOGEOGRAPHY OF THE ALEXANDER AND ASSOCIATED TERRANES

There have been several tectonic reconstructions proposed for plate boundaries and volcanic arc terranes associated with the North Cascades. One area of current research involves the evaluation of competing paleogeographic models for the Alexander terrane and associated volcanic arcs during Siluro-Devonian time (Wright and Wyld, 2006, Colpron et al, 2009, Cocks and Torsvik, 2011, and Beranek et al, 2013). These models can be evaluated independently using paleomagnetic results from the Alexander terrane- as well as for the major cratonal units. This presentation will focus on a reanalysis of paleomagnetic data from the Devonian Karheen Formation.

Red sandstones of the Lower-Middle Devonian Karheen Fm were sampled and studied by Butler et al, (1997) and by Grommé and Hillhouse (1995). Both groups collected from sites located on Prince of Wales Island in SE Alaska. The results of both paleomagnetic studies reported that samples with well-defined paleomagnetic directions pass both the paleomagnetic fold and reversals test, and thus are interpreted to have a magnetization that was acquired during, or shortly after, deposition. The available paleomagnetic and rock-magnetic data (see Butler et al, 1997) indicate the paleomagnetic signal in these sedimentary rocks is carried by hematite. The tilt-corrected mean direction reported by Butler et al, 1997 is D = 233, I = 26, which yields an estimated paleolatitude of 14 +/- 4. The shallow paleolatitude obtained for these rocks allows for either a northern or southern hemisphere option.

For magnetizations carried by hematite in sedimentary rocks the potential for paleomagnetic inclination error should be evaluated. Using the method of Tauxe and Kent (2004)- who utilize the ellipticity of directional data to estimate inclination error- a corrected mean I = 37 is indicated- placing the Karheen Fm at 20 +/- 5. These should be interpreted with caution due to the low number (29) of paleomagnetic sites used in this analysis. These results would appear to rule out the southern option for the Alexander terrane proposed by Wyld and Wright (2006). The higher paleolatitude resulting from this analysis would favor models such as Beranek et al, 2013, who place the Alexander and related arc terranes north of the Laurentian margin during mid-late Devonian time.