The Borromeo String Quartet certainly threw its newest member in at the deep end. Second violinist Kristopher Tong, playing his first major Boston concert with the ensemble, participated in the Borromeo's first complete live performance of Arnold Schoenberg's Fourth String Quartet on Sunday afternoon.
Tong, who at 24 is more than a decade younger than the other players, may look like their nephew who has dropped in for the weekend, but he is an animated, intelligent player who is already participating in the grownup discourse and not just tagging along. He also plays -- and listens -- with a physical involvement that is fun to watch. A great string quartet is always evolving, even when the personnel is stable; Tong, who joined the ensemble March 1, will contribute to the evolution, just as his two predecessors did.
A virtuoso exercise in composition, the fourth Schoenberg quartet seethes with invention and counterpoint, but it is also rich with chameleon substance. Schoenberg's last two quartets were premiered on concerts featuring late quartets of Beethoven; the expressive ambitions are comparable, although the language is different. But the music still exhibits a march step, dance rhythms, recitative and aria, the developmental recurrences of rondo themes. The individual players are hyperactive, the second violin at one point turning high arabesques above the first, but moving toward a common goal.
The performance wasn't entirely settled in, but the quality of engagement and the power of struggle were palpable, as was the triumph of many episodes, including the quiet close. First violinist Nicholas Kitchen sometimes helps the audience when difficult works are on the docket, but he didn't speak yesterday. That's too bad, because the Gardner Museum prefers supplying extended biographies of performers to offering musical information that could be helpful to listeners.
Anything would have sounded relaxed after the Schoenberg, and Dvorak's delightful 14th Quartet certainly did.