The Brooklyn Rider string quartet. (Sarah Small)

A wildly eclectic audience packed the Sixth & I Historic Synagogue on Saturday night as the classical-music cognoscenti sat cheek-by-aging-jowl with high school students and hipsters. But that’s to be expected in a concert by Brooklyn Rider, a young, adventurous string quartet devoted to keeping the traditional quartet repertoire alive while dragging the form — kicking and screaming, if necessary — into this century’s anything-goes postmodern world.

What makes the members of Rider particularly interesting is how they draw out the almost neural connections between composers and artists of different eras. Mendelssohn’s String Quartet No. 1 in E-flat, Op. 12 (an unabashedly romantic work), opened the evening, and the Riders gave it an extremely warm, glowing reading — maybe a bit smudgy in the details and lacking in bite, but deeply involving nonetheless. Their real point, however, was to underscore the ties between Mendelssohn and Beethoven — and then between Beethoven and such modern composers as John Zorn, whose quietly searing “Kol Nidre” and a stunning quartet from 2011 drew overtly from Beethoven’s quartets.

That kind of interconnectivity was the hallmark of the performance. Composer Christina Courtin drew on Stravinsky’s neoclassical period for her charming, dancelike “tralala,” and Dana Lyn was inspired by the visual artist Mierle Laderman Ukeles for her “Maintenance Music,” which used sliding microtones and jagged, repeated motifs to atmospheric (if slightly queasy) effect. The snapping fingers, stomping feet and final leap into the air of Vijay Iyer’s jazzy “Dig the Say” echoed the great James Brown, and Colin Jacobsen’s “Three Miniatures for String Quartet” created lush, Persian-flavored sound-gardens of extraordinary beauty.

But it was the two works by Zorn that — to these ears, anyway — really made the night. Zorn is one of the most imaginative and prodigiously gifted composers of any era, and his quartet “The Alchemist” is, simply put, a masterpiece — an absolute tour de force. Explosively inventive, deeply human, utterly fascinating from first note to last, the work is built around the theme of Beethoven’s famous Grosse Fuge, Op. 133, but takes it into freewheeling new realms.

The Riders — clearly committed to the work — gave it a breathtaking performance.

The Brooklyn Rider string quartet. (Sarah Small)