Magmas mix! What about the evidences?

Hi all. We know that magmas mix, mingle and do everything:) (It must be quite boring downstairs, so no surprise) What I'm asking is; you look at the product: examine the thin section of a say, volcanic rock, a basalt or andesite; what clues can you catch that might indicate magma mixing? And how do you combine them from clues you get by geochemical examination?