Chances are you have a pretty limited view of what "opera" is. That's understandable, since most of what's produced by major opera companies was written by a handful of 18th and 19th century European composers.

But it's a more stylistically diverse art form than you may imagine. Did you know there's a whole genre of mariachi opera, rooted in that Mexican folk style? And how about operas built around Argentine tango? And have you ever heard of a zarzuela? It's kind of like Spanish operetta or musical theater, complete with dance numbers.

You'd know all this if you greeted autumn Wednesday night at Minnesota Opera's season-opening "Opera Afuera." The first musical event to be presented at St. Paul's Allianz Field, home stadium of the Minnesota United soccer team ("the Loons" to you), it not only offered a cowbell-jangling audience a mini musical education but showed off some powerful voices that soared skyward, making for a very entertaining evening beneath a harvest moon.

Lest you picture 20,000 opera fans waving their scarves and shouting "Bravo!" Wednesday's crowd was but a fraction of that, assembled near the midfield stripe on the stadium's western edge. Before us were conductor Miguel Harth-Bedoya, the Minnesota Opera Orchestra and a modest stage, its lone scenery four rectangular screens adorned with Jackson Pollock-esque splashes of hot pink and yellow on a pattern suggesting soccer balls. The singers emerged from behind them to deliver 16 arias, duets and ensemble pieces.

As the twilight dimmed, so did our ability to see the performers, but the magic of video technology made them considerably clearer up on the scoreboard at the stadium's southern end. Soloists' hometowns and career highlights appeared there, too, in typical sports style.

The standouts were those who delivered something quite out of the ordinary for a night at the opera. Such as Vanessa Alonzo, an award-winning mariachi singer whose best work was accompanied not by the orchestra but by Twin Cities masters of the style Mariachi Mi Tierra. Alonzo's long-held high notes on "La Cigarra" and "La Malaguena" would have blown the roof off the place had there been one. And she bewitched with an aria from Jose "Pepe" Martinez's 2010 mariachi opera, "Cruzar la Cara de la Luna," in a role she originated and has revisited several times since.

Mariachi wasn't the only Latin American style on tap. There was an orchestral fugue from Astor Piazzolla's tango-driven "Maria de Buenos Aires" (which could have used more of a sizzling sense of danger), as well as scenes from Jimmy Lopez Bellido's "Bel Canto" and Daniel Catan's "Florencia en el Amazones" that left me hungry for more.

Those two operas gave us some of the evening's most intense drama, context rendered unnecessary by the passionate singing of Zoie Reams on an aria from "Bel Canto" and Vanessa Becerra and Andres Acosta on a duet of sorrowful parting from "Florencia."

And, for those longing for something more conventionally operatic, the Italians got their due with scenes from "Pagliacci" and "Rigoletto," while Becerra lent lovely lyricism to an excerpt from "La Boheme" and Reams' rich mezzo voice proved ideal for "Carmen," a work that will close Minnesota Opera's season next spring.

Rob Hubbard is a Twin Cities classical music critic. •