Trans-Hudson shear zone

The other striking feature is that ht is largest in the centre of the Western Superior and seems to diminish in magnitude towards the Trans-Hudson shear zone. In fact, there are a number of null measurements (no splitting) in the Trans-... 

In some ways the Superior Province appears different from other Archaean cratons worldwide. For example, it exhibits thicker than average crust and long uninterrupted geological belts, not commonly seen on other cratons. The Superior Province is also unusual in the sense that it exhibits very large shear-wave splitting values in the heart of the craton and very little in the surrounding Proterozoic Trans-Hudson shear zone. It is more normal for the surrounding mobile... 

Hudson shear zone (Silver Kaneshima 1993 Kay et al. 19996). One would perhaps expect more uniform values if the anisotropy is solely a result of SAF. Given the fact that the Trans-Hudson Orogeny was an event of Himalayan proportion, it is surprising that so little evidence for associated anisotropy exists. An alternate explanation is that the mantle is anisotropic but oriented in such a way that there is no apparent splitting (e.g. vertical orientation of the olivine a-axes). 

There are, however, interesting details that are to date unique to the Western Superior Provinee. These include thicker than normal Archaean crust, a slab-like velocity anomaly in the mantle transition zone, and large SKS splitting in the Archaean Superior Province but little spUtting in the surrounding Trans-Hudson Proterozoic shear zone. 

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