Often when popular performers start singing standards and touring with 70-piece orchestras it signals the beginning of the end of their creativity.

Last night at the FleetBoston Pavilion, folk icon Joni Mitchell's exquisite performance of Tin Pan Alley classics was simply the addition of another page to the rich and varied story of her musical life that spans folk, pop, jazz, avant garde, world music and now, with her latest release "Both Sides Now," a kind of large, economy-sized torch singing.

As her album does, the first part of Mitchell's two-hour performance tracked the movements of a love affair from first thrilling crush to dashed-on-the-rocks despair and after intermission healing and tentative hopefulness with the aid of 12 classic songs, including two of her own. As Mitchell put it, it was time to "put down the guitar, get away from the piano and just sing."

And sing she did in a voice that has become dusky and copper-edged with age. The 56-year-old Canadian native's soprano has gone from ethereal flute to smoky clarinet, its slight rasp and bright tone the perfect complement to these sepia-toned songs of jubilance and melancholy.

The night began softly with the brushed drums and gentle strings of "You're My Thrill" and Mitchell singing lines like "You send chills right through me" with palpable excitement.

Resplendent in an ornate and flowing red ankle-length coat, Mitchell made "At Last" a breezy caress with the aid of a bright and airy flute lending sweet charm.

The noir-ish "Comes Love" - with its swaggering after hours brass and muted, foreboding trumpet solo - was the first sign of danger on this romantic path and "You've Changed" began illuminating the dark shadows as Mitchell sang "the sparkle in your eyes has gone."

It continued from there with Mitchell heading to the bar for a conversational take on her own "A Case of You," blowing about in "Stormy Weather" and coming to the realization about the mercurial nature of life with her own "Both Sides Now."

Mitchell also performed another handful of her own tunes with the local orchestra's crisp accompaniment including satisfyingly boppy "Be Cool," and the bustling jazz of "Hejira" and her I hate show business folk classic "For the Roses."

Mitchell returned for an encore to a standing ovation.

Just as we were leaving to meet deadline obligation we heard her break into a sassy take on Marvin Gaye's "Trouble Man."