Zircons

Mahoney et al (1999) concluded that there was no plausible explanation for Archean zircons in the Baja BC province if the hypothesis was true. However, Housen and Beck (1999) argued that the zircon data supports the Baja BC hypothesis.

Figure 1 shows the histogram data of U-Pb ages of detrital zircons from Mahoney et al. (1999) and Mustard et al. (1995), and basement ages of North America modified from Hoffman (1989). The circles denote the positions of Baja BC relative to North America and the arrows denote the location of Baja BC during deposition of units where detrital zircon ages are available. Housen and Beck (1999) claim the decline in Grenville zircons in the upper units reflects the movement of Baja BC north, away from Grenville crust in southwestern North America.

Figure 1. (Housen and Beck 1999)

The Methow/Methow-Tyaugton basin, sedimentary basins within the Canadian Cordillera, can be linked to source regions to the east in the southern Canadian Cordillera. These results suggest the 3000-kilometer northward migration of Baja BC unlikely because there are no known southern source regions for the detrital zircon grains. The data are the result of high-resolution sampling and show significant heterogeneity (DeGraaff-Surpless et al. 2003). The figure below is a comparison of composite detrital zircon and signatures from Methow/Methow-Tyaighton strata with the potential Cordilleran source regions (Figure 2).

Figure 2. (DeGraaff-Surpless 2003)