The term 'HALF OF A 1960S QUARTET' can be solved by the crossword solution 'MAMAS'. This refers to the popular American vocal group, The Mamas and the Papas, who were active in the 1960s. The group was composed of four members: John Phillips, Denny Doherty, Michelle Phillips, and Cass Elliot. Therefore, the term 'HALF OF A 1960S QUARTET' is referring to any two of the four members of The Mamas and the Papas.