PREHEAT oven to 300°F if using a silver 9-inch springform pan (or to 275°F if using a dark nonstick 9-inch springform pan). Mix wafer crumbs and margarine. Remove 1/2 cup of the crumb mixture; set aside. Press remaining crumb mixture firmly onto bottom and 1-1/2 inches up side of pan. Refrigerate while preparing filling.
BEAT cream cheese, sugar and vanilla in large bowl with electric mixer on medium speed until well blended. Add eggs, 1 at a time, mixing on low speed after each addition just until blended. Remove 1 cup of the batter; place in medium bowl. Add chocolate and the reserved crumb mixture; mix well. Set aside. Stir orange zest into remaining batter; pour into prepared crust. Top with spoonfuls of the chocolate batter. Cut through batter with knife several times for marble effect.
BAKE 50 min. to 1 hour or until center is almost set. Run knife or metal spatula around rim of pan to loosen cake; cool before removing rim of pan. Refrigerate 4 hours or overnight. Store leftover cheesecake in refrigerator.