It is the Chekhover variation of the Sicilian Defence, so called because it was first played in a serious tournament by International Master Vitaly Chekhover (1908-1965) in a game against Lisitsin in Leningrad in 1938. It is characterised by 4. Qxd4 although, unlike your game, it is usually followed (after 4...Nc6) by 5. Bb5.
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