Dixie Chicks' Natalie Pasdar Files for Divorce from Husband Adrian

Dixie Chicks lead singer Natalie Pasdar has filed for divorce ... TMZ has learned.

Natalie cites irreconcilable differences in her petition to end her marriage with Adrian Pasdar. The couple has two boys, ages 16 and 12, and she's asking for joint custody.

Natalie and Adrian, an actor who starred in "Heroes," married back in 2000.

Sources connected with the couple tell TMZ the split is amicable.

It's ironic ... just last year a feature article appeared on a country music news site calling the couple one of "Country's Greatest Love Stories."