I suppose we need to qualify what constitutes an interracial marriage. In South America one is not guaranteed to have any Native or African ancestry, especially in the affluent families who are wealthy enough to marry royalty. This is partly due to the caste system in the Spanish colonies. Also, in countries like Argentina, there was a TINY native population, so the VAST majority of the gene pool is European--particularly Italian as a result of the golondrinas immigrants.
The same is true for the Native Americans in North America. Prestigious colonial families in New England and elsewhere did not intermarry with natives often, as it would have been seen as a negative mark on the family. Prestigious Virginian families almost NEVER married outside their own ranks, and cases like John Rolfe are the rare exception.
In particular areas at particular times, natives and Europeans married freely. For example, the Scottish Jacobite exiles living in the rural South (modern Georgia, South Carolina, and Tennessee) sometimes went west into the Cherokee and Creek nations, married and were assimilated into the culture. My father (who is an American) comes from one of these families, which are considered wholly Native American, and they still, despite their mixted ethnicity, only intermarry with other Scots-Cherokee families...mainstream European-American families rarely intermarried with Native American ones before the early twentieth century, and almost never outside of certain regions like Oklahoma and upstate New York.
As for the Greeks and Turks, that is indeed a funny issue. My mother is part Turkish...but when I look at the ethnic characteristics of modern Turks and compare them to the other modern Turkic tribes from Mongolia to Uzbekistan, I hardly believe that the Seljuks and Osmans never intermarried with Greeks. I can't imagine that the Ottomans kicked every last Byzantine out of Anatolia...and one can't help whom they fall in love with. ;-)
