Is a 10GHz clock required to drive a 10Gb serial pin?
On the Altera parts you provide some reference base clock like 156.25Mhz.   Then the transceiver section has a PLL that brings the frequency up to I think half the rate.   So it'll be 5 Ghz for for the 10Gb/s link.  Or it might be lower if instead of having one 10Gb/s link you break it into 4 lanes like we do for the XAUI interface.   That clock and the parallel data get fed into the serializer and out comes 10Gb/s serial data.    That's the gist of it anyway.   You can read more about how the Altera transceivers work here.

Here's an cut out from their documentation.