[dons even shinier geek hat]
The Elves never turned up at the Pelennor.
It's implied they fought to protect Lothlorien and Mirkwood (to protect their own realms), but they never fought any of the major battles. One of Tolkien's themes is that the elves were withdrawing from the world, leaving the mortals to their own devices. That's why Jackson's idea to have the elves turn up at Helm's Deep is still one of my pet peeves about the films -- it's contrary to a major theme in the story.
The elves only came to Minas Tirith with Arwen when the war was over.
[/removes geek hat & returns to Uruguay v Ghana]