Paleomagnetism of the Mount Stuart batholith revisited again: What has been learned since 1972?

Eocene rotation of the Coast Plutonic Complex and Intermontane Belt: paleomagnetism of Eocene plutons along the Klondike Highway

“…Various geological methods have been used to examine the conflict, such as paleontologic paleogeography (e.g., Smith 2006), detrital zircon age distributions (e.g., Mahoney et al 1999), and structural analysis (e.g., Gabrielse et al 2006;Wyld et al 2006); however, these methods have continued to yield estimates of *1000 ± 500 km for northward translation of the CPC relative to North America. Conversely, some paleomagnetic studies have continued to yield translation estimates of >2000 km (e.g., Housen et al 2003;Enkin et al 2006). Between these two polarized hypotheses, there have been studies seeking to find common ground.…”

“…Both mechanisms, because of the orientation of the APWP relative to the Cordillera, lead to an overestimation of the amount of northward translation (Symons et al 2005). Thirdly, Baja-BC tectonic models rely inherently on the paleomagnetic inclination data only (Irving 1985;Housen et al 2003;Enkin 2006), assuming that the discordance in declination is an unimportant consequence of vertical-axis rotations by ballbearing or distributed shear tectonics (Beck 1976(Beck , 1998Beck et al 2000).…”

“…Firstly, geologic evidence, such as known fault displacements, can only account for *1000 km of northward displacement (e.g., Gabrielse et al 2006), which is far less than the *2000 to *4000 km of post-mid-Cretaceous northward displacements often postulated (e.g., Beck 1980;Irving et al 1985Irving et al , 1996Wynne et al 1995;Johnston 2001;Housen et al 2003;Enkin 2006). Secondly, much of the paleomagnetic evidence for northward displacements of >2000 km comes from sedimentary strata that, unlike igneous rocks, are subject to inclination shallowing by compaction (Kodama 1997;Kodama and Ward 2001) and to easy remagnetization by interstitial meteoric and hydrothermal fluids (Oliver 1992;Symons et al 1999;Enkin et al 2000;Muttoni et al 2001).…”

“…By far the most significant criticism is that much of the Cordilleran paleomagnetic data comes from igneous intrusions that lack a known paleohorizontal from bedding, thereby rendering their paleoinclination less reliable , although paleohorizontal can often be constrained by host rock attitudes (e.g., Symons et al 2004), Al-in-hornblende geothermobarometry (Harris et al 1997(Harris et al , 1999Housen et al 2003), metamorphic contact aureoles (e.g., Bardoux and Irving 1989;Marquis and Irving 1990), dike attitudes (e.g., Symons 1969b;, etc. The second significant criticism is that a unit's ChRM in the general absence of clear contact tests is usually assumed to be primary and co-linear with the Earth's coeval magnetic field direction at the unit's original location.…”

“…In a study of the Spetch Creek pluton, Vandall (1993) found that the discordances in the then available CPC Cretaceous paleopoles could be well explained by a combination of 500 or 1000 km of northward translation plus 178 to 578 of clockwise rotation with minimal ENE-side up tilts of only *28. Building on an analysis by Beck (1992), paleomagnetists started to consider more carefully the temporal consequences on a pluton's ChRM from tilting and uplift by using Alin-hornblende geothermobarometry and combinations of radiometric age dating systems (Harris et al 1997;Butler et al 2002;Housen et al 2003). Also, utilizing the fact that the terranes forming a microplate should share a common APWP, while together, Symons et al (2005) and McCausland et al (2006) used both the declination and inclination remanence data for each unit to build an APWP for each terrane.…”