A snake bark maple (sorry, not sure which species, but if it's important I can dive into my reference books and find out) has an area of dead bark extending about half way around the tree and for a vertical distance of about a foot.

The tree is about 10 years old, trunk diameter about 4 inches (girth about 12inches), height about 12ft. It's in cold clay, gets waterlogged for a few hours at a time about half a dozen times a year, and is surrounded by various other small trees and large bushes. Until now, it's been growing healthily, and has flowered profusely for the last three years.

There is no sign of pest on the dead bark area, or any sign of weeping, visible fungus or anything else. It looks like the sort of damage you get when a couple of branches rub together, though this is obviously not the case here. One twiglet growing from the damaged area is dead, but the rest of the tree, both above and below the damaged area, seems fine.

Any ideas? I've googled but not found anything - most acer disease hits refer specifically to A palmatum, and adding 'snake bark' gets the sales hits.