Vibrant, assertive new music from the Flux string quartet

Named after the absurdist Fluxus art movement of the early ‘60s, the New York-based Flux Quartet is among the more invigorating, genre-expanding entities on the string quartet scene. Founding violinist Tom Chiu and his current confederates -- violinist Conrad Harris, violist Max Mandel and cellist Dave Eggar -- play with passion, crystalline focus and sprinkles of humor.

In 2003, the quartet made a splash, even beyond modest new-music circles, by taking on Morton Feldman’s infamous String Quartet II, an ultra-spare, mind- and time-expanding six-hour work. (The Kronos Quartet performed it in the ‘80s in a brisk four-hour model but quickly swore it off.) Monday at the Los Angeles County Museum of Art, the Flux presented an altogether different new-music picture, one that teemed with assertive -- even rocking -- sounds.

Although grounded in contemporary music, the program also delved into far, fuzzily defined corners of rock and jazz. Composer and avant-rock guitarist Elliott Sharp writes intense string music, the bowed equivalent of manic guitar strumming. His two-chord, vampish “Tesalation Row” generates a gritty, sawing ensemble tone, sounding like a big surrogate distorted guitar.

Composed by a jazz artist prone to shunning categories, Ornette Coleman’s “Poets and Writers” is continually evolving, making each performance a quasi-premiere. In its scattered construction and atmosphere of pleading lyricism are traces of Coleman’s “harmolodic” notions and also of his unique violin playing, somewhere between enlightened child’s play and devoted nonconformism.

Chiu’s own “SAS” seems inspired by Coleman’s concepts; it fudges the lines between score and improvisation and is built around rising and falling ensemble energies. Michael Byron’s “Awakening at the Inn of the Birds” is minimal without being Minimalist in the classic keep-your-riffs-running way. Its seductively swaying, almost breath-like waves of action are redolent of bagpipes or circular accordion textures.

The concert’s highlight came from a 20th century “old master,” Iannis Xenakis. His 1983 “Tetras” plays with the string quartet palette while sidestepping melodic or thematic concerns or even a fixed musical language. Instead, he explores varieties of gesture and noise potential, all tightly fashioned into a form suggesting an elaborate sound sculpture and/or ritualistic event.

The Flux amply proved its mettle with this tour de force, the brightest spot in a headily vibrant evening.