Thomas Mapfumo first came to prominence singing protest songs for the Zimbabwean independence movement during the 1970s and followed up with music of celebration and reconstruction after the 1980 overthrow of the Rhodesian colonial regime (an artistically crucial period well documented on his delicious Shumba: Vital Hits of Zimbabwe). Since then his music has continued to grow in richness and depth, with neither his rhythmic drive nor the restrained yodeling urgency of his singing losing any of their force. The peculiar fascination of chirmurenga, the idiom he developed, comes partly from a skipping rhythm that stands out as something distinct from what we Westerners usually hear in African pop music. This 12/8 pattern is based on arpeggiated figures played on the mbira (thumb piano with a large gourd resonator), a traditional instrument as central to chimurenga as the electric guitar is to rock and roll. Any performance by the Blacks Unlimited is a prime opportunity to hear some real thumb-piano virtuosity, the two mbira players being as important to the music as Mapfumo himself (especially on the roots numbers when the electric instruments all drop away, leaving Mapfumo, mbira players, and percussionists alone to demonstrate what it means to carry traditional forms of communication into a high-tech age). But Mapfumo, a riveting, subtle vocalist at the height of his powers, possesses a strangely offhand charisma and seems to dominate the proceedings almost in spite of himself. Saturday, Equator Club, 4715 N. Broadway; 728-2411.