Unfortunately Process Monitor does not yet support managed call stacks. But perfview is pretty good at decomposing managed stacks and it also provides a way to collect File I/O events:
Select File I/O events in Run/Collect dialog:
After tracing is finished you should have File I/O events available in the directory tree:
Double clicking it should present you a window with all collected File I/O operations
Each operation has a call stack registered and you may browse it on other tabs available in the events window.