R. Kelly Turns Himself In and Mug Shot Released After Sexual Abuse Arrest

R. Kelly just surrendered to police in Chicago ... turning himself in after being charged with sexual abuse of 4 girls, at least 3 of whom were minors.

The embattled R&B singer turned himself in Friday night at a Chicago police station.

As we reported ... prosecutors in Chicago hit Kelly with 10 counts of aggravated criminal sexual abuse Friday morning, and 9 of the 10 counts involve alleged victims ranging in age from 13 to 16 years old. There are 4 alleged victims in total, and one of them is the subject of 4 different counts.

According to the criminal complaint, the allegations include oral and vaginal sex with a girl between the ages of 13 and 17 ... and the allegations are extremely graphic.

Michael Avenatti says he's representing at least 1 of the alleged victims in the Kelly indictment ... and he says the new sex tape he turned over to prosecutors shows R. Kelly engaging in sex acts with a 14-year-old girl -- vaginal sex, oral sex, anal sex and urination.

Avenatti says he's planning to go after R. Kelly's enablers -- lawyers, managers, agents and others whom he says stood idly by and protected the singer as he sexually abused young girls. Avenatti's mission ... bringing them to justice.

Avenatti also claims Kelly's 2008 trial -- in which he was found not guilty -- was rigged by threats and payoffs.