The major place where grantic continental crust is manufactured is a. Over hot spots b. In rift valleys c. At convergent margins d. It was apparently all produced billions of years ago and is not produced under the present conditions of Earth Solution Answer is A. Materials are also added to continental crust through intrusive and extrusive igneous activity. Plumes of magma from the Earth\'s asthenosphere are generated from the friction produced at the contact zone where oceanic crust slides past continental crust. These plumes then rise upward into continental crust to form granitic plutons or a variety of volcanic features on the Earth\'s surface. A pluton can be defined as any igneous intrusion of rock that forms a kilometre or more below the Earth\'s surface..